The study investigated effects of family size on household food security in Osun state, Nigeria. Multistage sampling technique was employed to select 110 respondents for the study. A well structured questionnaire was used in collecting information from the respondents. The data were subjected to descriptive and Tobit regression analysis. The results of the study indicated that about 60.9% had family size of 5and 8 members. Only 24.5% were food secure. Coping strategies employed include borrowing money, relying on less preferred and less expensive food. The constraints faced includes, poor access to credit (84.5%), and lack of input (81.8%). The study concludes that large family size has negative impact on house food security. The study recommended that government and non government agency should intensified effort on importance of family planning and advocate small family size in rural area.