Shipments of Apple's iPads will fall behind the growing variety of tablets running Google's Android platform for the first time this year.
Smaller-sized devices are continuing to catch on with more consumers, research firm International Data Corp said today.
IPad shipments are expected to account for 46% of the market in 2013, down from 51% last year, IDC said.
Devices running Android are expected to grow their market share to 49% this year from 42% last year.
IDC also raised its 2013 tablet shipment forecast to 190.9 million units, up from its previous forecast of 172.4 million units. It did not say how many tablets were shipped last year.
Google's Nexus 7 tablet and Amazon.com's Kindle, which uses its own customisation of Android, were hits with consumers last year.
In November, Apple launched its own foray into smaller-sized tablets with the iPad mini.
"One in every two tablets shipped this quarter was below 8 inches in screen size. And in terms of shipments, we expect smaller tablets to continue growing in 2013 and beyond," IDC said in a press release.
Last month, Hewlett-Packard announced the launch of the Slate 7 tablet powered by Android, a centrepiece of that company's effort to expand in mobile devices and reduce its dependence on the shrinking personal computer market.
IDC said tablets running Microsoft's Windows 8 platform would grow their market share from 1% last year to 7.45% in 2017.
Tablets running the Windows RT operating system, which is not compatible with older software that runs on Windows, will see their market share stay below 3% until 2017, IDC said.
"Consumers aren't buying Windows RT's value proposition, and long term we think Microsoft and its partners would be better served by focusing their attention on improving Windows 8," IDC said.