The YouGov survey, commissioned by the End Violence Against Women (EVAW) coalition, found that 85 per cent of women between 18 and 24 had been sexually harassed, with half of this age group said they had experienced unwanted sexual touching.
Only 11 per cent reported that someone else had intervened on their behalf while being inappropriately touched, with eight in 10 saying they would have liked someone to have stepped into to help them.
Overall, the research found that 64 per cent of women of all ages had experienced harassment, with more than a third (35 per cent) experiencing inappropriate touching.
Sarah Green, acting director at the EVAW, said: "If women are planning their lives around not being harassed or assaulted, they are not free.
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"Women should be free to live their lives without the threat of harassment or violence, and not having to plan and limit their choices to make sure they are safe."
Later this month, EVAW will be launching a manifesto on ending violence against women and girls for the London mayoral candidates ahead of the city's election in May.
YouGov surveyed 1,650 adults in an online survey of which 889 were female and 106 were female aged 18-24.
The study was carried out between February 26 and March 1 this year.