Around 80% of Yahoo's revenues are derived from advertising, compared with rival messaging company America Online, which gets most of its revenues from subscribers to its ISP.
The new service is expected to work with different kinds of branded content in the background of the messages.
The software, however, will let users select screens that appeal to them, for example those that chiefly promote entertainment companies' products.
Users will also in some cases be able to link through to Yahoo's commerce site where they can buy products promoted in the instant messenger service.
Shares in Yahoo! rose 3.3% to $11.74 (£8.24) yesterday on Nasdaq. The shares have lost 81% over the past year.