Apple still had a solid lead and shipped more iPads worldwide than a year earlier. Monday's study came from IDC.
Apple had no new tablets out in the third quarter. It also might have seen sales slow amid expectations of an iPad Mini.
Apple could regain share in the holiday quarter with the new iPad devices.
In the July-September period, Apple shipped 14 million devices, up 26 per cent from 11 million a year ago.
Its market share fell as the overall tablet market grew by 50 per cent to nearly 28 million.