Joshua Wong, Nathan Law and Alex Chow were sent to prison last Thursday for their leading role in the initial protest that sparked the months-long Umbrella Movement of 2014.
Their jailing was slammed by international rights groups and politicians and prompted accusations that the independence of Hong Kong's courts has been compromised under pressure from Beijing.
Tens of thousands turned out in protest on Sunday.
Wong, sporting a newly shaven haircut in accordance with Hong Kong prison rules, was at High Court Tuesday as part of another case dating back to the Umbrella Movement.
He is one of 20 activists charged with contempt of court for violating an order to clear the Mong Kok protest camp - scene of some of the most violent clashes during the demonstrations.
In closing arguments prosecutor Victor Dawes said that by obstructing bailiffs the defendants had intended to 'interfere with the administration of justice' which amounted to criminal contempt.
Dawes added that the large crowd meant there were safety and public order concerns.
Supporters packed the courtroom and the areas outside.
Veteran activist Leung Kwok-hung, known as Long Hair shouted: 'They have Rimsky Yuen -- you have the Hong Kong people!' before the case began, referring to the city's justice minister at the centre of the controversy over the jailings.
Joshua and fellow defendant Raphael Wong, who is also in custody, responded with a cheer from the dock, surrounded by four uniformed guards.
Hong Kong people and lawmakers march through the streets wearing prison uniforms as a statement in support of imprisoned student political activists Joshua Wong Source: AAP
Hong Kong was returned from Britain to China in 1997 under a 'one country, two systems' arrangement, guaranteeing freedoms unseen on the mainland, but there are growing concerns those rights are disappearing as an assertive Beijing tightens its grip.
The government has vehemently denied there was political interference in the decision by the Court of Appeal last week to overturn previous non-custodial terms for Wong, Law and Chow and instead jail them for six to eight months after a sentencing review brought by the department of justice.
Prosecutors have filed a raft of cases against pro-democracy activists with fears that more will be jailed in the wake of last week's judgement.
Lester Shum, another prominent Umbrella Movement activist and one of the defendants in court Tuesday, said before the hearing that he felt relaxed about his case, adding he was inspired by the 'determined attitude' of other jailed activists.
