Crop diversification has several economic, social and environmental benefits for smallholder farmers. It Increases farm household income and employment opportunities for farmworkers, improve conservation of natural resources, soil fertility, improve food and nutrition security, and reduces output production shortages. While productivity is constrained by many factors such as technology, resources, environment, socio-economic, infrastructure, and crop pests and insects, food insecurity and malnutrition were Ethiopia's main development challenges. In Sinana District, agriculture is traditional malnutrition is devastating problems, particularly for the poor and unprivileged households. The study builds on the basic assumption that crop diversification plays essential roles in improving household food and nutrition security in rural Ethiopia. The overall objective of the study was to analyze crop diversification, food and nutrition security among wheat dominant producer rural households in Sinana District Bale Zone, Ethiopia. The study is positioned in the pragmatism philosophical assumption that applies to mixed methods research. It focused on primary data that was generated through cross-sectional survey. The cross-sectional survey was conducted using semi-structured questionnaire, Household food Insecurity Access Scale, household dietary diversity questionnaire, anthropometric data, key informant interviews, focus-group discussion and field observations. The study sample size was 384 households. Multistage sampling was employed to study subjects at different scale. STATA software version 14.2 was used to analyze data. Descriptive and inferential statistics and econometric models were used to analyze data. A Craggâ€™s Double Hurdle model used for measuring the probability, extent and determinants of crop diversification practices of rural households. Ordinary least squares regression model used to analyze the effect of crop diversification on household food security while multinomial logistic and Zero-truncated Poisson regression model were used to analyze determinants of household food insecurity and the determinants of household dietary diversity respectively. Pearson correlation coefficients were calculated to see the correlation between the nutritional security status indicators and the crop diversification index. Univariate and multivariate logistic regression were performed to identify factors associated with infant nutrition. The result reveal that the average crop diversification index of sampled households was 41.3 percent. The probability of crop diversification was positively influenced by household size, access to fertile farm plots, and access to extension services and negatively influenced by age of household head, and participation in off/non-farm activities. The extent of crop diversification is positively affected by access to extension services, labor availability, membership to farmers cooperatives, and distance to market. The diversification of crops has had a positive and significant effect on household food security. Although crop diversification has been positively associated with household food security, several other factors have been shown to be equally or more important in increasing household food security. Household education, access to irrigation system, owned livestock, total income and remittances have had a positive impact on household food security. Analysis of household dietary diversity has shown that almost all respondents consumed food made from cereal, while only 20.1 percent, 10.2 percent and 7.3 percent of the household consumed egg, meat and fruits in the previous seven days of a survey, respectively. On average, household consumed 5.7 food groups. About 13.5 percent, 50.5 percent, and 35.9 percent of the participants consumed low, medium, and high dietary diversity level, respectively. Education level, participating in irrigation farming, membership to farmersâ€™ cooperatives, farm size and livestock holding positively affected household dietary diversity, while remoteness from the nearest market and remittances negatively impacted household dietary diversity. The prevalence of malnutritionrnvirnparticularly stunting (23.8 percent), underweight (21.2 percent) and wasting (9.5 percent), respectively. Crop diversification is negatively correlated with stunting and wasting and positively with underweight and children's dietary diversity score. Child nutritional status is strongly associated with age of household head, maternal and parental education, farm land size, livestock owned, availability of drinking water, sex of children, and dietary diversity of children, family access to sanitation, total annual income and family access to health services. Any effort to increase household food and nutrition security should consider empowerment of farmers through adequate training and informal education, enhancing crop diversification. Policy and development interventions should target intensive agricultural production, rural infrastructure development, and education and awareness tools to be provided. Families update nutritional knowledge and agricultural technologies to increase production and income, and thus improve family nutritional security.