The decline is the sixth consecutive fall registered by the utilities this year, according to the data released by the Federation of Electric Power Companies.
Nuclear power generation from the country fell 60.4% to 9.63 billion kWh as three reactors at Tokyo Electric Power (TEPCO) and Hokkaido Electric Power remained offline in August.
The electricity generated by fossil fuel-fired plants fell 8.2% to 53.7 billion kWh.
The data revealed that the utility rate of nuclear power plants, including those at Japan Atomic Power, fell 43.8 points on the year to a record-low 26.4% because of the safety concerns following the 11 March 2011, nuclear disaster.
Nuclear disaster led to the shut down of many reactors and others are offline for regular maintenance and their restarts have been delayed, reports Nikkei.
Power output from TEPCO and Tohoku Electric Power fell by 17.7% to 25.9 billion kWh and 18.1% to 6.81 billion kWh, respectively.
