The research by the Zero Tolerance Charitable Trust found one in three girls also thought forcing a woman to have sex was acceptable in some circumstances. Academics from Glasgow and North London universities carried out the research, which included a survey of 2,039 young people aged 14 to 21 in Glasgow, Manchester and Fife.
The researchers found one in five young men thought forcing his wife to have sex would be acceptable, while one in seven agreed it would be justifiable in a long-term relationship.
One in 10 thought there was nothing wrong with raping a woman if the man was "so turned on he can't stop", while one in six of the boys thought he might personally force a woman to have sex. Nearly one in ten said he would rape a woman "if nobody would find out".
In total, the findings meant half of all those surveyed had said rape was acceptable in one set of circumstances.
The academics who carried out the research said they were shocked by the results. "It was shattering," said Sheila Burton of North London University.
The researchers also studied attitudes to violence towards women and found one in four young men thought hitting a woman could be justified if she had "slept with someone else".
And one in eight said it would be OK to hit a "nagging" woman, while one in 10 said hitting a "disrespectful" woman was justified.