About 10,000 people have gathered in central Bangkok to protest the continuing influence of the military in politics, even after the country returned to civilian rule.
The protesters on Sunday demanded the government of Prime Minister Prayut Chan-o-cha end its heavy-handed approach and parliament be dissolved.
Prayut led a military coup six years ago and served as head of the interim government. He has remained in the post following a general election last year.
The protesters also called for a new constitution to replace the one that came into force under the interim government.
Some protesters openly spoke about the monarchy at rallies despite a law that bans insulting the royal family.
Anti-government protests have spread across the country since an opposition party was disbanded in February. The party had opposed military involvement in politics.
Police arrested rally participants on charges of sedition.