Cow milk is a daily produced high value product that plays a significant role for both home consumption and income generating. However, in the selling of raw milk marketed supply, the producers do not attain potential gains. Thus, this study attempted to identifying factors affecting farmers’ decision to participate and determinants of the level of cow milk marketable surplus supply in Gemechis district. Both primary and secondary sources were used to collect data. Data were collected from a sample of 152 cow milk producers were analyzed through STATA ver. 15. Double hurdle model was applied. The first-hurdle model estimation result demonstrated that education level, distance to district market, the proportion of land allocated for forage production, size of milk output per day, access to milk market information, and frequency of extension contact influences farmers’ decision to participate in cow milk market. The second-hurdle model results investigated that children under six years, the proportion of land allocated for forage production, size of milk output per day and access to credit were significantly affects the level of cow milk marketable surplus supply. Therefore, the study recommends that emphasis should have to give on encouraging flow of milk market information, intensification of land use, and enabling farmers as they produce more through improving production and productivity of cow.