NGOs, like any business or government organizations, experience staff turnover which in turn affect their organizational performance. AMREF Kisii County is one of the leading NGOs working in improving the health situation of the country. The general objective of the study is to investigate the impact of staff turnover on the organizational performance of AMREF health Africa Kisii County and to forward possible recommendations. In order to conduct the study, explanatory design was followed. All professional staff members of AMREF found in the head office are included in the study. Questionnaires were administered for 43 staff members and a semi-structured interview was conducted with four senior staff members of the organization. Document found in the organization was reviewed. The data collected through questionnaires were analyzed and interpreted using frequencies, percentages, mean values and standard deviations, regression and correlations. Information collected through interviews was analyzed qualitatively. The study revealed that the major factors for staff turnover are related to payment and incentives, and training & development factors. The study has shown that on the major strategic intervention areas, the organizational performance of AMREF has been found very low. In relation to staff susceptibility for staff turnover, the research finding depicts that AMREF lost its very experienced staff members which has been affecting the organizational performance negatively. The other finding of the study is that AMREF doesn’t have a specific retention strategy which can be implemented practically to address the problem of staff turnover.