The court said Ivi, which operates streaming website ivi.ru, had labelled the Italian comedy "Perfect Strangers" with a 16+ rating, breaking Russia's strict laws banning the promotion of "non-traditional" relations to children.
Russia toughened its anti-LGBT laws last year, allowing authorities to fine any individual or organisation found to have promoted homosexuality in public, online, or in films, books or advertising.
Ivi said it would study the court's ruling and make a decision about whether to appeal.
"We continue to be proactive with our content base and ensure that all content on our platform is correctly labelled," it said.
Russia's tougher restrictions have caused confusion among streaming sites. Policing content can require trawling through hours and hours of footage to check for material that could violate the new rules.
Cases can be initiated by state communications regulator Roskomnadzor without warning, a source familiar with the matter told Reuters.
Ivi is one of more than a dozen streaming sites in Russia to be fined or threatened with penalties this year for showing LGBT content without an 18+ rating, the RIA news agency has reported.
Kinopoisk, a streaming service owned by Nasdaq-listed tech giant Yandex, was fined 1 million roubles this month for incorrectly labelling some films. Yandex argued that the films could only be watched via subscription and were available only to viewers over 18.
Lawmakers argue that Russia's laws are necessary to protect society from what they see as decadent "Western values".
Rights groups say the laws are designed to outlaw representations of lesbians, gay men, bisexuals and transgender people (LGBT) in public life.
($1 = 90.0475 roubles)
(Reporting by Caleb Davis and Alexander Marrow; Additional reporting by Alessandro Parodi; Editing by Gareth Jones)
By Caleb Davis and Alexander Marrow
