No financial terms were disclosed.
Google Toolbar is a software program users install inside a browser, allowing them to more quickly search the Web than by having to visit Google.com each time they wish to do a search.
The deal, which builds on an existing two-year distribution pact between Google and RealNetworks, is the latest pact Google has signed with major computer hardware and software companies to distribute its software.
In recent months, Google has set deals with PC maker Dell Inc. and software maker Adobe Systems Inc.
By ensuring wide availability of its Web search software, Google is racing to head off competition from Microsoft as it moves later this year or early next year to release Vista.
The companies said that the Google Toolbar and Mozilla Firefox browser will soon be made available as options for customers of RealPlayer, RealNetwork's Rhapsody music subscription service and RealArcade games.