Sweet potato value addition is increasingly being popularized among producers due to its potential to reduce wastage, increase market access and fetch optimal prices. Despite these documented benefits, smallholder sweet potato producers in Kenya have not implemented value addition widely. This study analyzed the factors influencing value addition and extent of value addition by smallholder sweet potato farmers of Rachuonyo South sub-county in western Kenya. Using a sample of 200 smallholder farmers, Heckman’s Probit model with sample selection was employed to firstly identify the factors affecting a farmer’s decision to adopt value addition, and secondly evaluate the factors that affect the extent of a farmer’s participation in sweet potato value addition. Study findings show that the probability of adoption was significantly influenced by household size, total quantity produced, credit access, land size and training. Further results show that the distance to the market, group membership, credit access and total quantity produced were found to greatly influence the extent of value addition by sweet potato farmers. In order to leverage smallholder farmers’ adoption of sweet potato value addition, it is important that county and national government policies should focus on encouraging farmers’ group formation, provision of cheap value addition loan packages, seminars, farmer field days and workshops to enable exchange of ideas among different farmers and further encourage farmers to produce more to benefit from economies of scale. In addition, proper marketing strategies such as linking farmers with supermarkets, adequate product development, proper packaging and labeling are challenges that require urgent attention.