The purpose of this study was to investigate the effect of IFMIS on cash management practices in the public service. This has been necessitated by the fact that the use of IFMIS in the public service is undergoing challenges with many users experiencing problems with certain complicated features of IFMIS coupled with security, flexibility and reliability issues that have an impact on efficient cash management in the public service. The study was based on the Contingency theory and descriptive survey research design was employed. The study focused on70 staff and top management at the Eldoret West District treasury. Questionnaires and interview schedules were used to collect primary data. Data was analyzed using descriptive statistics, regression and correlation. Study findings showed that reliability of IFMIS, Flexibility of IFMIS positively affect cash management. The findings also showed that a reliable system is basically one that is accurate, timely, complete and consistent in collection of information and the infrastructure which supports the IFMIS is supposed to be secure from destruction, corruption, unauthorized access and breach of confidentiality so that there is efficient cash management. Flexibility of local IFMIS design can decrease chances of failure in cash management. Findings also revealed that the implementation of IFMIS has not been a success as a result of the top down management exhibited in most of the public services. There is need for public service to ensure that the information generated by IFMIS is consistent without delays and undue changes that demand further manual help. Public service should tailor information concerning IFMIS in such a way that it cannot be tampered with by others. Also, there should be sufficient IFMIS controls to curb tampering. Public service should also ensure that IFMIS easily adapts to the changes in cash management without complete overhaul of the system.