Research firm IDC said global tablet sales for the full year rose just 4.4 percent to 229.6 million units, after a jump of more than 50 percent in 2013.
After the euphoria around tablets in 2013, the market has slowed because consumers are keeping their devices longer and turning in some cases to large "phablet" smartphones or new "ultramobile" PCs.
The fourth quarter saw the first year-over-year decline in sales since the first iPads were released in 2010, according to IDC. Overall sales dipped 3.2 percent in the key holiday quarter compared to a year earlier to 76.1 million units.
A separate survey by Strategy Analytics said quarterly tablet sales hit 78.3 million, a slim gain of one percent.
"The iPhone 6 (Review | Pictures) products are putting pressure on the iPad mini and the continued success of the Mac could be inhibiting some iPad Air 2 growth," said Eric Smith, analyst at Strategy Analytics.
But IDC said the market could pick up again this year.
"Despite an apparent slowdown of the market, we maintain our forecast about tablet growth in 2015," said Jean Philippe Bouchard, an IDC analyst.
"Microsoft's new OS, a general shift toward larger screen form factor and productivity focused solutions, and technology innovations such as gesture interface that could be introduced in tablets will help the market maintain positive growth in 2015."
Apple remained the top seller in the quarter with a market share of 28.1 percent, according to IDC, and 27 percent according to Strategy Analytics, even though iPad sales were down 18 percent.
Samsung was the number two seller with a 14.5 percent share, IDC said.
The IDC report said China's Lenovo was third with a 4.8 percent share and Taiwan's Asus fourth with 4.0 percent.
According to IDC, Amazon which does not release precise tablet sales figures was in fifth place with a 2.3 percent share, but sales of its Kindle Fire tablets slid 70 percent from a year earlier in the past quarter to 1.7 million units.
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