This study computes the regional total-factor energy efficiency (TFEE) in Japan by employing the data envelopment analysis (DEA). A dataset of 47 prefectures in Japan for the period 1993-2003 is constructed. There are 14 inputs, including three production factors (labor employment, private, and public capital stocks) and 11 energy sources (electric power for commercial and industrial use, electric power for residential use, gasoline, kerosene, heavy oil, light oil, city gas, butane gas, propane gas, coal, and coke). GDP is the sole output. Following Fukao and Yue [2000. Regional factor inputs and convergence in Japan-how much can we apply closed economy neoclassical growth models? Economic Review 51, 136-151 (in Japanese)], data on private and public capital stocks are extended. All the nominal variables are transformed into real variables, taking into consideration the 1995 price level. For kerosene, gas oil, heavy oil, butane gas, coal, and coke, there are a few prefectures with TFEEs less than 0.7. The five most inefficient prefectures are Niigata, Wakayama, Hyogo, Chiba, and Yamaguchi. Inland regions and most regions along the Sea of Japan are efficient in energy use. Most of the inefficient prefectures that are developing mainly upon energy-intensive industries are located along the Pacific Belt Zone. A U-shaped relation similar to the environmental Kuznets curve (EKC) is discovered between energy efficiency and per capita income for the regions in Japan.