All digital copies of films added to users' UltraViolet collections will now carry BBFC age ratings.
UltraViolet is a "cloud-based" system in which customers add participating films to their collection via a code.
Films can then be streamed over the internet, or downloaded, onto mobile devices.
"The flexibility of UltraViolet makes it even more important for users to be able to make informed decisions about what they stream or download, particularly if they have children in their care that might be using the service," said David Cooke, the director of the BBFC.
BBFC age ratings will also be displayed on UltraViolet parental control functions, allowing parents to password protect content.
The BBFC has also reported a sharp rise in "online only" works being submitted for classification.
Unlike films in cinemas and on DVD, ratings for online only content are not required by law. Examples include drama series House Of Cards, which premiered on internet streaming service Netflix.
New figures, revealed on Thursday, showed that, up to 1 September 2013, online only classifications are up 135% on the same period in 2012.
Presenting the BBFC's annual report in July, Cooke said that while the internet downloads did not fall under BBFC's remit - but could be submitted voluntarily - it was "becoming clearer that both politicians and the public want us to play a role".