She said he had been "palling around" with an ex-member of US-based militant group Weather Underground, which opposed the Vietnam War in the 1960s.
Mr Obama once served on a charity board with a member of the group, but he has denounced its activities.
The group was blamed for a number of bombings in the US in the 1960s.
Mrs Palin described Mr Obama as someone who saw the US "as being so imperfect... he is palling around with terrorists who would target their own country".
Mr Obama served on a charity board several years ago with Mr Ayers, who is now a professor at the University of Illinois.
The White House hopeful, who was a child when Weather Underground was active, has denounced Mr Ayers' radical past.
Is this a reaction to the negative response to her 'folksiness' in the V.P. debate?
Whatever, it is disappointing to see such transparent tactics being used. No-one is naive enough to think dirty tactics don't make up part of such a campaign, but attacking a candidates credentials and/or policy is different to character smears. I don't think this will work out well either for Palin or for the Republican campaign.
My apologies if this has already been posted.
Edited by Leonardo, 05 October 2008 - 10:01 AM.