Adverts placed in the widgets will be targeted to specific keywords, in the same way as Google's traditional web adverts.
However, the search giant will measure the effectiveness of the ads by how much user interaction they produce, rather than how many click-throughs are achieved.
Photo-sharing website Slide started the trend to monetise the applications when it said last month that it would include ads in its widgets.
Slide's widgets are the most widely used on the web, according to audience measurement analyst comScore Media Metrix.
The small pieces of software, which Google and Microsoft refer to as 'gadgets' rather than widgets, add features to websites or to software such as the Google Desktop application.
Google currently offers more than 14,000 individual widgets, including a BBC Radio player, a calculator, an English to Tamil dictionary and a Champions League football information portal.
Around 87 million Americans used an online widget in June, according to figures from comScore Media Metrix.
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