The software will be available starting Wednesday. It requires a $100-a-year subscription to Office and won't be sold separately.
The new offering follows the release of an iPhone version in June and brings an Office app to phones running the most widely used operating system on new smartphones.
Microsoft Corp. is trying to make its Office 365 subscription more compelling, without removing an advantage that tablet computers running Microsoft's Windows system now have - the ability to run popular Office programs such as Word, Excel and PowerPoint.
"The release of this app shows that we're committed to keep providing additional value for Office 365 subscribers," the company wrote in a blog post. "Office 365 subscribers will now be able to access, view, and edit Word, Excel and PowerPoint documents with Windows Phone, iPhone and Android phones."
(Also see: Microsoft Office for iPhone app review)
Microsoft is pushing subscriptions as a way to get customers to keep paying for a product that was historically sold in a single purchase. The company touts such benefits as the ability to run the package on multiple computers and get updates for free on a regular basis. However, a subscription can be more expensive than buying the package outright for just one or two computers.
Microsoft said it designed Office Mobile for Android phones specifically for small-screen devices, even though many people will prefer editing documents on a tablet's larger screen. The company has a version for iPads and Android tablets, called Office Web Apps, but that runs on a Web browser and requires a constant online connection. The new Android software is an app that gets installed on the phone and can work offline.
With a subscription, customers typically get to use Office on up to 10 devices. Five of them can be Windows or Mac computers or Windows tablets. The other five can be iPhones or Android phones. Windows phones come with Office installed and do not count toward the limit.
In keeping the software off the iPad, the top-selling tablet computer, Forrester Research analyst J.P. Gownder has estimated that Microsoft is potentially ceding $1.4 billion a year in revenue, based on 10 percent of the 140 million iPad owners paying for a $100 subscription. Gownder said failure to provide it on the iPad or Android tablets gives incentives for users to explore competing offerings such as QuickOffice from Google and iWork from Apple.
Like the other mobile versions, the new Android software is designed for lightweight use. For example, you can use it to view and edit an attachment sent by email. But it's not meant to create a complex spreadsheet from scratch.
The new software requires Android 4.0 or later - the Ice Cream Sandwich or Jelly Bean flavors of Google's operating system. It's available through Google's online Play store. At first, it's available only in the U.S., though Microsoft plans to expand to 117 markets with versions in more than 30 languages.
Microsoft did not announce any plans for BlackBerry phones.