The study found that not only do they lose their virginity earlier, but are also likely to engage in risky sex by not taking precaution.
The six-year study of more than 1,200 teens on the effect of sex in films on younger teenagers was published in journal 'Psychological Science', the 'Daily Mail' reported.
Researchers from Dartmouth College and Ivy League university in the US, surveyed 684 top-grossing movies from 1998 to 2004, and then coded them for sexual content.
A film such as 'Eyes Wide Shut' would be coded highly, while 'Lord Of The Rings: The Return Of The King' would get a low coding.
The researchers then recruited 1,228 youngsters aged between 12 and 14, and each one was asked which films on the list they had seen from a number of different collections of the 50 randomly selected movies.
Six years later, the same participants were surveyed to find out how old they were when they became sexually active and how risky their sexual behaviour might have been.
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The results showed that exposure to sexual content in movies at an early age is likely to influence adolescents' sexual behaviour.
"Much research has shown that adolescents' sexual attitudes and behaviours are influenced by media. But the role of movies has been somewhat neglected, despite other findings that movies are more influential than TV or music," lead researcher, Dr Ross O'Hara, said.
"Adolescents who are exposed to more sexual content in movies start having sex at younger ages, have more sexual partners, and are less likely to use condoms with casual sexual partners," said O'Hara.
"These movies appear to fundamentally influence their personality through changes in sensation-seeking, which has far-reaching implications for all of their risk-taking behaviours," he said.
The study refers to sexual content in films but campaigners against on-line porn say it could equally apply to videos on the internet.
They point out that children can now see a lot more sexual imagery online than they ever did at the cinema