The Nikkei 225 index at the Tokyo Stock Exchange fell 101.01 points to 8,552.81. The Topix index of all first-section issues sank 5.98 points, or 0.80 percent, to 740.71.
The euro remained weak against the dollar in Asia on Tuesday after sinking to a 10-week low on rating agencies' warning that a deal by European leaders may not be enough to fix the region's debt crisis.
European Union leaders last week agreed on a pact designed to tighten fiscal discipline and economic union within the bloc, but criticisms by credit-rating companies sent European and US stocks as well as the euro tumbling.
The Nikkei was down amid growing concerns over further potential downgrades of European sovereign debt, said Hideyuki Ishiguro, supervisor of investment strategy at Okasan Securities.
Moody's said the debt talks had offered "few new measures" and that the crisis remains in a "critical and volatile stage".
It said it would review ratings of all European Union nations early next year in the light of their failure to come up with the measures it believed necessary to tame the eurozone debt crisis.
Fitch Ratings warned that "market tension remains high" and predicted a "significant" economic downturn in Europe.
In Tokyo trading, exporters with major business in Europe fell, with Nikon down 2.19 percent at 1,691 yen and Canon down 1.00 percent at 3,465.
Olympus shares rose 5.38 percent to 1,370 yen as fears faded that it might be delisted. The company is expected to file a financial report Wednesday in time for the deadline to avoid delisting.