This research was carried out with the objectives of examining the key Determinants of Diffusionrnof Online Payment Systems in Addis Ababa and the relationship among these key determinants inrnthe case of potential adopter buyers and potential adopter sellers. It used the five characteristicsrnof innovation â€“ relative advantage, compatibility, simplicity, trialability and observability â€“ ofrnthe Diffusion of Innovations Theory (DIT) by Everett M. Rogers. Questionnaires were distributedrnand 342 from potential adopter buyers and 96 from potential adopter sellers were finally usedrnfor analysis using SPSS software. Frequency distributions were checked to summarizerndemographic profiles, correlation analysis was used to examine the relationship among keyrndeterminants of diffusion and multiple regression analysis were used to check the effect ofrninnovation attributes on the diffusion of online payment system in Addis Ababa. The results showrnthat, for the case of potential adopter buyers, only compatibility, trialability and observabilityrnwere found to be significantly determining diffusion of online payment system in a positiverndirection and for the case of potential adopter sellers, only relative advantage has shown arnsignificant influence which was positive. The determinants were also found to have a positivernrelationship among each other. As a result, the researcher recommends that banks or otherrnfinancial institutions that will be given the task to facilitate online payment system shall operaternin accordance with the findings by focusing on compatibility, trialability and observability whenrndesigning marketing programs for potential adopter buyers and focus on relative advantagernfeatures when designing marketing programs for potential adopter sellers.