Occupy Movement student leader Joshua Wong was on Wednesday jailed for three months for contempt of court.
He was among 16 activists who either pleaded guilty or were found guilty of ignoring a court injunction during the clearance of the Mong Kok Occupy protest site in November 2014.
High Court Judge Andrew Chan said Joshua Wong's involvement on the day was deep and extensive.
Raphael Wong, the vice-chairman of the League of Social Democrats, was given four and a half months in prison for his "active" role in obstructing court bailiffs.
Both the activists were sent to prison by the court in the afternoon after it rejected pleas from the defence for a delay in sentence execution.
The other defendants, including the then-student leader Lester Shum, were given suspended jail sentences. Some of them wiped away tears of joy when they learned they were being spared time behind bars.
Speaking before the sentencing, Joshua Wong, 21, said he was prepared to be jailed again and had no regrets about taking part in the Occupy movement.
"They can lock up our bodies, but they can't lock up our minds. Even though we need to face the prison sentencing, we'll still continue to fight for democracy in the future," he said.
Shum said he had no regrets over his actions. "I'm still proud of my involvement in the Umbrella movement," he said, while Raphael Wong urged Occupy supporters to vote in the March by-elections for four Legco seats left vacant by the disqualification of pro-democracy lawmakers.
Earlier, supporters of the activists gathered outside the court shouting slogans calling for universal suffrage.
A further four Occupy protesters who pleaded guilty to contempt of court had already been sentenced, receiving one-month suspended prison terms and fines of HK$10,000.
Joshua Wong was on bail before the sentencing, with an appeal underway against a six-month prison term he received last August over a separate case.
That jail sentence was handed down after the government successfully challenged the non-custodial punishments the Demosisto leader, party colleague Nathan Law and former student leader Alex Chow, were originally given relating to an earlier protest in 2014.
Last updated: 2018-01-17 HKT 17:19