Hundreds of former Somali military members have vowed to fight any foreign peacekeepers who set foot in the Horn of Africa country.
Wednesday's protest in the capital, Mogadishu, was organized by former soldiers who served in Somalia's last formal army before the country fell into chaos in 1991.
The demonstration took place one day after a group of East African nations said they would send troops to Somalia as peacekeepers.
Somalia's weak interim government, based in the town of Baidoa, has requested the troops. But Islamists who control the capital and much of southern Somalia strongly oppose any peacekeeping force.
The Islamists organized their own protest in Mogadishu Tuesday, drawing several thousand people.
Somalia has not had a national army or an effective central authority since the fall of the last government more than 15 years ago.
Earlier this week, Islamist officials and the government agreed to eventually form a national army and to oppose any foreign intervention. The sides are to hold further talks beginning in late October.
Some information for this report was provided by AFP and AP.