The main stock index edged down 0.18 percent, or 11.38 points, to 6,451.68. It had closed at 6,463.06 on Friday, the highest since May 23, Reuters data showed.
Foreign investors accounted for around 54 percent of the day's turnover of 750.45 million rupees ($5.93 million), which was below this year's daily average of 1.05 billion rupees.
The bourse saw a net foreign inflow of 342.3 million rupees, extending year-to-date inflows to 14 billion rupees.
"The market is running on foreign buying. We will see continuous foreign buying with a bit of corrections," said a stockbroker asking not to be named.
The market's 14-day Relative Strength Index (RSI) was still in overbought territory, at 75.673 on Monday and has been above the upper neutral level of 70 since April 16, Thomson Reuters data showed.
Retail profit-taking pulled the banking index by 0.18 percent down, led by Commercial Bank of Ceylon which fell 1.05 percent.
Analysts, however, said falling interest rates helped investors to be still optimistic about the market.
The island nation's central bank unexpectedly cut its key monetary policy rates by 50 basis points on May 10 to boost economic growth in the face of subdued demand and the market interest rates have been falling since then.
The rupee ended weaker at 126.20/55 per dollar from Friday's close of 126.45/50 on importer and bank demand for the greenback, dealers said.
($1 = 126.5250 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Subhranshu Sahu)