Police used tear gas and water cannons with chemical-laced water to disperse protesters who had cut through wire barricades that separated them from police lines outside parliament.
The Thai parliament has rejected a draft to amend the Constitution that includes changes in articles relating to the monarchy.
The student-led democracy movement has gained steam in recent months as it puts pressure on Prime Minister Prayuth Chan-ocha to resign and to make Thai King Maha Vajiralongkorn more accountable, according to the BBC.
After about six hours of chaos, a protest leader announced the end of the protest, saying the demonstrators had captured enough ground to declare they had achieved their goal of surrounding Parliament.
At least 41 people have been hurt during protests in Thailand's capital Bangkok, including five with gunshot wounds. "Maybe they are not that strong but they are a good stunt", said a 27-year-old protester named Earn as she posed for a photo with three of the ducks.
The group posted pictures of riot police on Twitter with the caption "Dictator's lackeys!"
As a large group of young protesters converged on parliament to present their demands for democratic reforms at around 2pm on November 17, police warned them to stay back before starting to fire water cannons for several minutes.
"The National Police Office wants to warn protesters that if you demonstrate peacefully then there is no problem, but if you destroy public property police will have to prosecute", Yingyos Thepjamnong, national police spokesman, told reporters.
MPs are also considering the role of the Senate, which was entirely selected by Prime Minister Prayuth's former junta and helped ensure that he kept power with a parliamentary majority after a disputed election previous year. Prayuth led the 2014 coup that overthrew the democratically elected government.
Police used dump trucks, concrete blocks and razor wire to barricade the building, while many demonstrators wore helmets, goggles and gas masks. "This is the first time it has happened where it has been mildly violent".
The Royal Palace has made no comment since the protests began, although the king himself recently described Thailand as a "land of compromise" when asked about the protests.
By 3:30 p.m. local time, about half of parliament had voted; nearly all of the senators and coalition party members had either abstained from making a decision or rejected the iLaw proposal. Prayuth's supporters have a majority in the parliament, where the entire upper house Senate was appointed by the junta he led after a 2014 coup until a disputed election a year ago.
Prime Minister Prayuth took power as the head of a military junta in 2014 and remained in office after an election a year ago.
Only one of seven proposals for constitutional reform would potentially allow amending the role of the monarchy, which protesters say has enabled decades of military domination in the Southeast Asian country.
Pro-democracy protesters in Thailand rallied again on Saturday, promoting a diversity of causes and taking an opportunity to display their rejection of the country's power structure directly to the monarch.
On Tuesday, Thailand experienced its most violent protests in months as protesters clashed with police officials.