This paper is an attempt to measure the economic efficiency of Dedza smallholder Irish potato (Solanum tuberosum) farmers in Malawi using a translog cost frontier, inefficiency effect model and input Elasticities from Seeming Unrelated Regression Model for asystem of cost share equations for labour, fertilizer, seed and land. A sample of 200 farmers has been considered from Dedza district in Malawi. Results indicate that the mean economic efficiency of Irish potato production in Dedza District is 0.61 with scores ranging between 0.12 and 0.94. The economic efficiency differences are significantly explained by non-farm employment, education, credit access, farm experience, degree of specialization, household size and frequency of weeding. The highest input substitution existed between labour and fertilizer, followed by seedfertilizer.