The banking sector in Kenya has benefitted from the advancement of information solutions that has shaped the operational processes. Kenyan banking sector has adopted the use of self-service technology (SST) as a tool of increasing the efficiency and effectiveness in most business processes leading to an increase in sales, profits and relative growth in market share of most companies. The aim of this study was to determine the effect of SST on operational performance of commercial banks in Nakuru County, Kenya. The specific objectives of the study were: to establish the effect of automated teller machines (ATMs) usage on operational performance of the banks, to examine the effect of Internet banking on operational performance of the banks and to determine the effect of mobile banking on operational performance of the banks.The study employed correlational-cross-sectional survey design. The target population comprised 31 of the commercial banks. A sample of 28 commercial banks was used in the study. Primary data was collected using structured questionnaires from operations and IT managers. The questionnaires were self-administered. The data collected was analyzed using SPSS version 20. The data was summarized using frequencies, means and standard deviations. The research hypotheses were tested using Pearson Product-Moment correlation and multiple regression. The study revealed a significant positive relationship between automated teller machines usage and operational performance, the study also revealed a significant positive relationship between internet banking and operational performance; further the study also revealed a significant positive relationship between mobile banking and operational performance. The findings revealed that the combined effect of SST on operational performance was significant. The findings also revealed that among the SST, mobile banking had the greatest relationship with operational performance. The study therefore concluded that SST positively and significantly influences operational performance of commercial banks in Nakuru County.