Following two periods of regulatory reforms in 1996 and in 2000, there has been rapid progress in restructuring Japan's electricity industry. The purpose of this study is to analyse the effect of the regulatory reforms on the technical efficiencies of electric power companies. Our findings show that first-period reforms implemented in 1996-1999 were able to decrease costs by 7.5%, while second-period reforms, during the period of 2000 to 2002, effectively cut costs by 11.8% with respect to the base costs before regulatory reforms.