* Loss attributed to ord shareholders 909 mln vs 497 mln estimate
* Posts Q4 loss of 0.64 yuan per ADS vs 1.26 yuan loss in 2016
* Shares fall almost 7 pct in pre-market trade
* Full-year revenue up 40.3 pct, beating estimates (Adds context, detail from release, share reaction, quote)
March 2 (Reuters) - JD.com Inc, China's second largest e-commerce firm, saw its stock drop on lower-than-expected quarterly profits on Friday, as the company's margins were squeezed by competition during its top earnings season.
JD.com's U.S.-listed stock was down almost 7 percent in pre-market trading.
Despite posting better-than-expected revenue for the quarter, the loss attributable to ordinary shareholders was 909 million yuan versus analyst estimates of a 463 million yuan loss.
China's saturated urban e-commerce market continues to create competitive pressure between JD.com and rival Alibaba Group Holding Ltd.
"Although we believe JD.com will survive in the severe competition of the e-commerce space in China, backed by its alliance with Tencent, we think it will be difficult for the firm to pass market leader Alibaba," said Chelsea Tam, analyst at Morningstar Equity Research in a note ahead of the earnings.
JD.com owns an extensive logistics network and is popular for fast delivery and retail sales, while Alibaba is light on assets and draws a large part of its sales from third party marketplace site Taobao.com.
Revenue for the quarter was 110.2 billion yuan ($17.38 billion), JD.com said, above analysts' mean estimate of 108.5 billion according to Thomson Reuters I/B/E/S.
The firm posted a 40.3 percent increase in full-year revenue to 362.3 billion yuan compared to 260.1 billion yuan a year earlier.
JD.com posted a loss of 0.64 yuan per American depository share, compared with a loss of 1.26 yuan a year earlier.
Marketing costs for the quarter squeezed JD.com's margins, rising 35 percent to 4.7 billion yuan, revealing the steep cost of competitive advertising during the November Singles' Day festival. (Reporting by Cate Cadell in Beijing, Munsif Vengattil in Bengaluru; Editing by Shounak Dasgupta and Elaine Hardcastle)