Hundreds of demonstrators took part in the march against laws prohibiting insult to Thailand's king.
The organizers of the rally called for the crowds to disperse as protesters moved from the Democracy Monument.
Those that remained clashed with police, according to reports, including some who threw paint and homemade explosives at officers.
Protesting the lese-majeste
The recent detention of four activists sparked Saturday's protests.
Authorities remanded the four in custody on charges of insulting the monarchy during last year's anti-government protests.
Those suspected of insulting the monarchy are subject to up to 15 years in prison under Thailand's lese-majeste law. Activists believe that the government has used the law for decades to crack down on political opposition.
Led by former military junta leader Prayuth Chan-ocha, the Thai government denies the protester's accusations.
Since November, Thailand has charged more than 58 people with lese-majeste, according to rights group Thai Lawyers for Human Rights
Thailand is a constitutional monarchy, where the king has a special status as the protector of the Buddhist religion.
Led by students
Thailand's student-led pro-democracy movement began last year, calling for the government's resignation and reforms to the monarchy.
Activists argue that the king has acquired too much power since he took the throne in 2016, following his father's death.
The surge of Covid-19 cases in Thailand slowed down the student movement.
The Royal Palace has not commented on the protests, but authorities consider criticism of the king unlawful.Dapatkan update berita pilihan dan breaking news setiap hari dari Kompas.com. Mari bergabung di Grup Telegram "Kompas.com News Update", caranya klik link https://t.me/kompascomupdate, kemudian join. Anda harus install aplikasi Telegram terlebih dulu di ponsel.