Small scale irrigation is one of the most useful irrigation systems designed to increase production and productivity. Despite these, however, smallholder farmers in the study area are not using small scale irrigation schemes. Therefore, the study was focused on assessing the determinants of small scale irrigation practice and its effect on household farm income in Yilmanadensa woreda. The total population in the selected four kebeles of the woreda was stratified in to two strata (irrigation user and non-user). Then two stage sampling was employed to select sample respondents. Results are based on data collected from a survey of 178 randomly selected rural farm households. Descriptive statistics and Heckman’s two-stage estimation methods were employed. The result shows that access to market information, sex of the household head, access to extension service, education level of the household head and distance from households’ residence to the nearest market are important determinants for small scale irrigation practice. The analysis further revealed that access to irrigation, access to credit service, total livestock holding and distance of the household residence from the nearest market is significantly associated with household total farm income. Generally improving access to market information, gender equality, access to extension service and education level of the household is better to enhance small scale irrigation practice which in turn improves households total farm income.