Non-Qataris can now own up to 25 percent of any of the 30 firms listed on the DSM, the Economy Ministry said in a statement carried on the official Qatar News Agency.
Previously, citizens of Gulf Arab states could not invest in the banking and financial services sectors. Other foreign investors could only trade in two companies, including market heavyweight Qatar Telecom.
Qatar, a staunch US ally and wealthy energy producer, is trying to attract foreign investment to diversify its economy.
Most other Gulf bourses provide limited access to foreign investors. In Saudi Arabia, the Arab world's largest market, non-Saudis can only invest through mutual funds.
On Thursday, capitalisation on the DSM stood at 47.2 million Qatar riyals ($12.97 million). The bourse's capitalisation for 2003 was 97.2 billion riyals.