The February contract slipped 3.9 yen, or 2.97 percent, to 127.3 yen. Other contracts closed down 1.9 to 2.4 yen.
"To judge the outlook for the market, we will have to see how the February contract expires tomorrow," said Naoki Shinohara, analyst at Kanetsu Asset Management.
Sentiment could deteriorate if the February contract expires at a price below January's, which expired at 124.9 yen, he said.
Rubber futures have been driven up by technical factors after Japanese fund operators squeezed short-positions, traders said.
The short-squeezing drove up the key contract to a four-month high of 146.9 yen a week ago.
The distant July contract has dropped 7 percent since hitting the high as long position holders squared up, traders said.
"There are very few fundamental factors right now," said a trader at a Japanese commodities house.
"The wintering dry season in Thailand and China's buying continue to be key fundamental incentives, but we have to see the outcome of tomorrow's expiration before making the next move."
The technical trend of the market should stay if the key distant contract sustains 134.8 yen, its 100-day moving average.
Kanetsu's Shinohara said the key contract could rise above 140 yen again if it held support after the expiry.
Turnover in TOCOM rubber was 17,954 contracts, compared with 15,443 on Friday.
Open interest stood at 55,822 lots as of the end of Friday against 54,968 on Thursday.
Open interest has jumped nearly 60 percent since the start of the year, a possible sign more investors are back in the market.
But many traders believe the gains were caused by technical factors, noting that open interest has risen since the exchange cut margins and contract units by 50 percent from late January.