Background rn Ethiopia, like most Countries in Sub-Saharan Africa, is experiencing rapid population growth.rnThe rapid growth prevents national development effort and affects maternal and child health.rnMoreover, the desire to realize the issues pertaining to small family size and harmonize the raternof population growth with socio-economic development in order to reach a high level ofrnwelfare can be achieved, if factors which affect family size are well identified. Differentrnfactors influence family size at different levels in different Societies. This Study assessedrnfactors affecting family size preferences in Assela town where data was not available in thisrnregard. rnObjective: To determine desired family size and identify factors influencing family sizernamong residents of Assela town, Oromia National Regional State, Ethiopia. rnMethodology: A Community Based Cross-sectional Study was conducted in Assela town,rnbetween March 25 and April 4, 2013. The town has 14 kebeles out of which 5 kebeles werernselected randomly. Systematic random sampling was used to select the study subjects. Samplernsize required for this study was calculated based on two population proportion comparisonrnformula and with 100% response rate a total of 214 couples were included in the study. Thernage of women ranged from 15 to 49 years and men above15 years. Data was collected afterrninformation was provided and informed consent was obtained. Similar questions were posed tornthe couplesâ€™ simultaneously but in separate locations and at distance they couldnâ€™t hear eachrnother. The quality of data was controlled at different levels. The desired family size wasrndetermined using mean score. Respondents were asked to determine which factors wererninfluential on their desired family size. Multiple linear regressions were used to seernrelationship between influential factors and desired family size. Associations of variables wererntested by using 95% confidence interval (C.I) and regression coefficient. rnResults: Mean desired family size for the study population was 3.8.Mean desired family sizernfor men and women were 4.1 and 3.5 respectively. The factors which had got higher magnitudernand rank included household income, sex preference and psychological factors. rnConclusion: It is quite possible that increasing educational level and age at marriage mightrninfluence couples to desire lower family size. It is possible that child sex preference andrnpsychological factors might influence couples to desire higher family size.