Low adoption of modern agricultural technologies amongst farmers in Nigeria has been identified as one of the main reasons for the low agricultural productivity and increase in poverty level. The general objective of this study is to examine the welfare impact of farm households adoption of improved cassava varieties in Southwestern (SW) Nigeria using poverty as an indicator. It utilizes cross-sectional farm household level data collected in 2013 from a randomly selected sample of 312 cassava producing households (186 in Ogun State and 126 in Osun State). The data obtained were subjected to descriptive and inferential statistical analysis such as Foster, Greer and Thorbecke (FGT) poverty measure and Logit regression model. The results revealed that adoption of improved cassava varieties increases the annual income and the annual consumption expenditure of producing households' thus increasing welfare in the SW Nigeria. An analysis of the determinants of adoption with logistic regression model showed that access to improved cassava cuttings within the villages, use of radio, farming experience and farming as a major occupation are significant factors influencing adoption of improved cassava varieties in the study area. In order to achieve the much desired poverty reduction and generate an improvement in farming households' welfare in SW Nigeria, efforts should be intensified in ensuring that farmers have access to adequate improved cassava cuttings at the right time and place. All programs, strategies and policies that would promote farmers' education on the technology and consequently lead to improved adoption should be pursued.