UPDATE 1-Alibaba Q2 jumps; trading volumes seen slowing

(Updates with details, changes dateline)

BEIJING/HONG KONG, Aug 27 (Reuters) - Alibaba.com Ltd (1688.HK) more than doubled its second-quarter net profit, boosted by interest income from its IPO proceeds, but China's leading e-commerce firm faces slowing global trading volumes.

The focus for Alibaba, which operates an online business-to-business site connecting small- and medium-size traders, is shifting from international to domestic trades as the global economy remains uncertain.

Alibaba, whose parent, Alibaba Group, is 39 percent-owned by Yahoo Inc (YHOO.O), posted April-June net profit of 396.46 million yuan ($57.87 million), a 159 percent increase from 153.14 million yuan a year earlier, and well above a 285.03 million yuan forecast by three analysts polled by Reuters Estimates.

"For the next six months, conditions (for Chinese exporters) will get tougher," CEO David Wei a conference call.

Alibaba's shares debuted in Hong Kong last November in a $1.49 billion IPO, the city's most popular initial public offer, but the stock fell nearly a third in April-June amid concerns about premium membership growth as U.S. economic woes spread.

The benchmark Hang Seng Index .HSI fell 3.3 percent in April-June.

As of end-June, Alibaba's combined marketplaces had just over 368,000 paying members, an increase of 44 percent on a year earlier. ($=6.84 yuan) (Reporting by Kirby Chien, Editing by Ian Geoghegan)