The proportion of its total user base that is female grew by 6% in the 11 months to November 2007, according to research firm comScore.
Only one women's lifestyle website, iVillage.co.uk, has more monthly visitors, at 3.49 million, according to November comScore data.
Hellomagazine.com attracted 1.05 million users in November; Handbag.com attracted 1.45 million.
The statistics bring the total female audience for Auto Trader across the magazine, mobile and web platforms to more than 1.9 million.
Auto Trader also has more female unique users than eBay Motors (1,117,000), MSN Autos UK (360,000) and Yahoo Autos (231,000).
Meanwhile, user-profiling research carried out by Auto Trader and eDigital Research shows that 42% of female users have a household income of £30,000 or more, while one in three women spend 30 minutes on the site per visit.