The Supreme Court ruling reverses a landmark 2009 Delhi High Court order which had decriminalised homosexual acts.
The court said it was up to parliament to legislate on the issue.
According to Section 377, a 153-year-old colonial-era law, a same-sex relationship is an “unnatural offence” and punishable by a 10-year jail term.
Several political, social and religious groups had petitioned the Supreme Court to have the law reinstated in the wake of the 2009 court ruling.
Correspondents say although the law has rarely – if ever – been used to prosecute anyone for consensual sex, it has often been used by the police to harass homosexuals.
Also, in deeply conservative India, homosexuality is a taboo and many people still regard same-sex relationships as illegitimate.
The BBC’s Sanjoy Majumder in Delhi says some politicians have spoken out against the court decision – but many believe it is going to be difficult for them to take on the anti-gay lobby.
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Source: BBC News