Those already idled for regular checkups must pass the first stage of the "stress tests" before restarting.
Chief Cabinet Secretary Yukio Edano told a news conference the tests would be based on standards proposed by the European Union following Japan's March 11 9-magnitude earthquake and tsunami, Kyodo News reported.
CNN reported the effort is designed to win public confidence.
"In addition to the existing mechanism, we have decided to introduce a safety evaluation based on new procedures and rules," Edano said.
Under the new rules, the 18 nuclear reactors idled for maintenance checks since the March 11 disaster must pass the stress tests before resuming operations. The tests would include computer simulations to determine the facilities' ability to withstand various natural disasters.
The country has 54 nuclear reactors.
The second round of tests will be done on all nuclear plants, officials said.
The results will be reviewed by the government Nuclear and Industrial Safety Agency and the independent Nuclear Safety Commission.