Extension support is essential for effective delivery of improved agricultural technologies. This study investigated the effectiveness of improved cassava production technologies and the requisite of extension delivery on it in Osun State, Nigeria. Specifically, the study identified the improved cassava production technologies disseminated to farmers. All the fifty extension personnel in the State Agricultural Development Project (ADP) were purposively interviewed. Data were summarized with frequency counts, percentages and means. Correlation coefficient was used for hypothesis testing. Result show that the following extension services were offered to famers in the study area: extension services, fertilizer procurement, agrochemicals, cooperative facilities, social networks, tractor hiring services, credit facilities, improved planting materials and marketing. The mean age of Extension Agents (EAs) was 44±7.11. About 84% of the Extension Agents were males while 16% were females. All the EAs had post-secondary education, while 92% of them had spent more than 10 years on the job. The mean fortnightly session training attendance was 18.22 ±8.93 over the past one year. The extension contact with farmers was low. Almost 89% of the EAs claimed to have disseminated all the cassava production technologies to farmers. Also, a positive and significant association existed between effectiveness of the improved technologies and EAs’ years of experience (r = 0.303; p<0.05) and the number of training had with farmers (r = 0.323; p<0.05). It was recommended that Extension Agents’ training and retraining programmes should be intensified so as to ensure effectiveness of improved cassava technologies