This study focused on the influence of procurement staff familiarity on sustainable public procurement adoption in Uganda factoring in the mediation effect of procurement ethical behavior. A quantitative descriptive cross-sectional research design was used in line with the ontology of objectivism and epistemology of positivism. Through the use of stratified sampling design, 259 respondents were selected to form a sample of the study out of the population of 790 civil servants. The respondents comprised of Chief Procurement Officers, Senior Procurement Officers, Assistant Procurement Officers, Inventory Management Officers, and Assistant Inventory Management Officers. A self-administered questionnaire approach was used to collect data from these respondents. The Structural Equation Model was used as the appropriate approach to analyze the data. Within this approach, factor as well as regression analyses were incorporated to ascertain the predictors and their level of prediction on the dependent variable. Additionally, the mediation analysis was carried out to establish the quality of the mediation effect that procurement ethical behavior has on the relationship between procurement staff familiarity and sustainable public procurement adoption. Results from the analysis indicate that procurement staff familiarity has significant direct and indirect influence on sustainable public procurement adoption. The indirect effect is through procurement ethical behavior. This further means that procurement ethical behavior has a significant mediation effect in the influence of procurement staff familiarity on sustainable public procurement adoption in Uganda. Based on these results, it is recommended that, the government of Uganda and the PDEs should invest and support procurement staff training programs to build the competence and confidence of the staff to adopt and participate in sustainable public procurement practices.