The study aims to measure technical efficiency, identify factors influencing participation decisions in Small-scale Irrigation (SSI), and its effect on potato farmers' technical efficiency and household income in the Lemu Bilbilo district, Arsi zone, Oromia region, Ethiopia. The study employed a multistage sampling procedure to select a total of 371 households from the Lemu Bilbilo district. Descriptive statistics and econometrics models (stochastic frontier model and endogenous switching regression model) were employed to achieve research objectives. The findings of the stochastic frontier model (SFA) show that potato output was positively and significantly influenced by input variables seed, land, labor, and Nitrogen, Phosphorus and Sulfur fertilizer. The findings of the probit model show that participation in SSI was positively affected by education, total livestock owned, farm size, extension contact, and cooperative membership whereas age of household, market distance, and irrigation water distance influenced participation in SSI negatively. Finally, the endogenous switching regression model result showed that if irrigators had decided not to irrigate, their average income and technical efficiency would have decreased by 19617.97 ETB and 0.16%, respectively. The differences were statistically significant at 1% probability level. On the contrary, if non-irrigators had decided to irrigate, their average income would have increased by 8240.41 ETB, and their technical efficiency would have increased by 0.06%. These differences were found to be statistically significant at 1% significance level. The study recommends that policymakers and development organizations should consider small-scale irrigation as a key strategy for increasing smallholder farmers' technical efficiency and household income. In addition, the study calls for government and institutional support in education, training, extension services, infrastructure (especially market access), and cooperatives.