Tokyo stocks opened 0.51 percent lower on Monday with investors jittery over the situation in Ukraine after Crimea voted to join Russia in a referendum rejected by the United States and the European Union.
The Nikkei 225-index, which lost 3.30 percent Friday, shed 73.34 points to 14,254.32 at the start.
"The Crimean vote was not totally unexpected, but does nothing to defuse geopolitical tension in the region, which will continue to bear on global equities markets for the time being," said SMBC Nikko Securities general manager of equities Hiroichi Nishi.
Investors will also be watching Chinese economic data as well as a two-day policy meeting of the US Federal Reserve on Tuesday and Wednesday.
Partial results with more than half the ballots counted in Crimea showed 95.5 percent of voters were in favour of leaving Ukraine, in the most radical redrawing of Europe's map since Kosovo's 2008 declaration of independence from Serbia.
US President Barack Obama hinted at possible additional sanctions on Russia, warning his Russian counterpart Vladimir Putin that the United States and its allies would "never" recognise Crimea's breakaway vote.
And the European Union was getting set to unfurl sanctions against Moscow.
The yen, considered a safe haven in times of uncertainty, has recently risen against the dollar and euro because of international tensions over Crimea.
The dollar was at 101.41 yen early Monday compared with 101.36 yen in New York Friday afternoon.
The euro bought $1.3904 and 141.02 yen against $1.3906 and 140.73 yen in US trade.
-- Dow Jones Newswires contributed to this article --