Just 11.7 per cent of the firm's UK partners are female, 2 per cent lower than the next worst performer Linklaters.
The survey, by Winmark Research and Inspirational Development Coaching, covered 50 top UK firms.
A Freshfields spokesperson said: “Four out of eight of our practice group heads in London are female. However, we do recognise that there is a problem, and the work-life balance is something we've been looking into for the last 12 months.”
Of the magic circle, Allen & Overy is the most female-friendly – of 172 London partners 32, or 19 per cent, are women. At Clifford Chance the figure is 16 per cent, at Slaughter and May 15 per cent and at Linklaters 14 per cent.
The national firms fared well, as did technology specialists Bird & Bird and Olswang, both with partnerships that are more than 30 per cent female. Lovells also scored highly, with a partnership that is 24 per cent female.
However, the survey was skewed by the fact that it did not distinguish between equity and salaried partners.
Slaughters and Simmons & Simmons both contributed to a UK Government report published in late 2001 by the Competition Commission's Denise Kingsmill. The report looked at women and the glass ceiling, and found that women working full time still only earn 81 per cent of their male counterparts' salaries.