Nowadays, Community Based Health Insurance (CBHI) become a promising avenue to protect households in the informal sector from high unexpected health expenditure. Since 2011, Ethiopian government had launched CBHI through piloting the program in 13 districts. Though promising results achieved in the program piloting, huge variation was observed in terms of enrollment, dropout and uptake among the pilot districts. The general objective of this study was to identify the demographic and socioeconomic factors which determine uptake of CBHI in Deder district, Oromia. Mixed reach design was preferred to conduct the current study in order to achieve the sated objectives. Both quantitative and qualitative data were administered. Quantitative data were collected from 182 participants (97 CBHI members and 85 dropout) using systematic random sampling and five CBHI members were purposely selected and administered for qualitative data. Questionnaire was administered for demographic and socioeconomic data and qualitative data collection guideline was developed to conduct interview. Frequency, percentage and Pearson correlation test was used to determine the relationship between variables in the quantitative and trend analysis was used to summarize the qualitative data. The finding revealed that householdâ€™s age, family size and education level had significantly and positively related to the uptake of CBHI. Result showed that participating in CBHI related meeting, understanding the importance of CBHI program, trust in CBHI administration, and occurrence of illness and availability of quality service were significantly and positively related to enrollment increase. Whereas, delay in membership card provision and distance to health facilities are significantly and negatively related to CBHI enrollment. Overall, the findings of this study illustrate a need for continuous awareness creation to improve CBHI enrollment, to involve communities in CBHI meeting such as general assembly and to mobile resources for improving the scheme capacity in delivering CBHI membership card within one month period according to the scheme bylaw.