In addition to three IPOs that raised 2.5 billion rupees there was another listing through introduction.
The Colombo Stock Exchange said its All Share Index closed up 5.9 percent by end May.
Out of 293 listed firms, 49 companies have given returns of over 20 percent to investors, 51 companies between 10 and 20 percent and 37 companies showing gains of between 5 and 10 percent.
Sri Lanka's companies are recovering from credit boom, which generated a stock bubble helped by margin trading and a balance of payments crisis in 2011.
Banks are still purging bad loans acquired during the bubble, but interest rates are falling.
Foreign investors who sold out during the bubble are now returning selectively picking well managed stocks.