The majority of those surveyed thought that 30 per cent or fewer state school pupils attended the universities. And 56 per cent of respondents believed it was more expensive to study at Oxbridge.
In fact, they charge the same tuition fees as the vast majority of other English universities and also offer some of the most generous bursaries.
Just over half (54 per cent) said they would generally recommend their brightest students to apply to Oxbridge, while 45 per cent said they would never or rarely do so.
Sir Peter Lampl, chairman of the Sutton Trust, said: "The misconceptions among secondary school teachers about Oxbridge are alarming and clearly have an impact on the number of bright state school students applying to these two great universities, despite the considerable efforts that both are making to reach out to them."
The Sutton Trust sponsors summer schools and other access initiatives at both universities for state school students and teachers.