The Nikkei index opened in positive territory but lost 0.19 percent, 18.48 points, to close the early session at 9,573.04. The Topix index also dropped 0.24 percent, or 2.04 points, to 839.25.
The mood of the market remained cautious ahead of a heavy week of US earnings reports, said Yumi Nishimura, deputy general manager of investment strategy at Daiwa Securities.
Major US corporate titans preparing for earnings releases include Morgan Stanley, General Electric, Verizon, IBM and Apple and Intel.
Players also sought further clues as to how corporate outlooks have been impacted by the 9.0-magnitude earthquake and deadly tsunami that caused the world's worst nuclear accident since the 1986 Chernobyl explosion, she added.
A lack of fresh leads also discouraged buying while the yen's relative strength weighed on sentiment, said analysts.
The Japanese unit stood at 82.95 to the dollar and 119.35 to the euro, against 83.09 and 119.91 respectively in New York.
Tokyo Electric Power Co's roadmap for a cold shutdown at its troubled Fukushima Daiichi nuclear plant was not seen enough to lift overall market sentiment, said Kenichi Hirano, operating officer at Tachibana Securities.
"While laying out a timeline is a positive, the timeframe could also be viewed as too long," he said, noting the utility's six- to nine-month schedule for the shutdown.
TEPCO shares added 0.21 percent to end the early session at 470, compared to above 2,000 yen before March 11.
Number-two telecom firm KDDI dropped 0.60 percent to 498,000 on a report that TEPCO was preparing to sell its stake to help fund compensation claims stemming from the nuclear accident.
Exporters were under selling pressure. Sony lost 0.98 percent to 2,437. Toyota Motor fell 0.31 percent to 3,230.