Alex Chow, 26, Nathan Law, 24, and Joshua Wong, the 20-year-old bespectacled student dubbed Hong Kong's "face of protest", were sentenced by the Court of Appeals to between six and eight months' imprisonment each, reports the Guardian.
The three had avoided jail a year ago after being convicted of taking part in or inciting an "illegal assembly" that helped spark the umbrella protests in September 2014.
But this month, Hong Kong's Department of Justice called for those sentences to be reconsidered, with one senior prosecutor attacking the "rather dangerous" leniency he claimed had been shown to the activists.
"See you soon," Wong tweeted shortly after the verdict was announced.
"Imprisoning us will not extinguish Hongkonger's desire for universal suffrage. We are stronger, more determined, and we will win.
"You can lock up our bodies, but not our minds! We want democracy in Hong Kong. And we will not give up," Wong said in a series of tweets.
The decision to increase the activists' punishments has sparked widespread outrage, the Guardian reported.
"It smacks of political imprisonment, plain and simple," said Jason Ng, the author of Umbrellas in Bloom, a book about Hong Kong's youth protest movement.
There was also criticism from the United States where Republican senator Marco Rubio attacked the decision as "shameful and further evidence that Hong Kong's cherished autonomy is precipitously eroding".
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
About VDC
Doraiah Chowdary Vundavally is a Software engineer at VTech . He is the news editor of SocialNews.XYZ and Freelance writer-contributes Telugu and English Columns on Films, Politics, and Gossips. He is the primary contributor for South Cinema Section of SocialNews.XYZ. His mission is to help to develop SocialNews.XYZ into a News website that has no bias or judgement towards any.