"This is part of an ongoing experiment to look at how we market across all media channels," said eBay spokesman Hani Durzy.
AdWords is Google's advertising system that shows ads based on words in Web searches and is the source of virtually all of Google's revenues.
Technology trade publication Computerworld, which originally reported the move, cited a source as saying it was in response to Google's decision to hold a party starting at the same time as an eBay conference for merchants who sell on its site.
The Google event, called the Checkout Freedom Party, is part of an effort to lobby eBay to accept its online payment system, known as Checkout, which competes with eBay's PayPal.
Durzy acknowledged that eBay was disappointed about the Google event. "We don't view that kind of activity as an appropriate activity for one partner to do to another."