The Fanli investment comes about a month after Rakuten bought U.S. eBook company OverDrive for about $410 million (274 million pound). Other high-profile acquisitions in recent years have included free messaging application Viber for $900 million and Canadian e-book reader Kobo for $315 million.
Rakuten did not disclose the size of the stake it bought in Fanli or how much it paid, and a spokesman declined to comment further. The investment valued Fanli at about $1 billion, according to a Rakuten statement.
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Kevin Johnson, the chief executive officer of Ebates, a U.S.-based online discount operator that Rakuten bought for $1 billion last year, will join Fanli's board of directors, the company said.
Rakuten already offers online services such as financing, travel, shopping and online video. It also announced last year it would set up a Japanese low-cost carrier with Malaysian budget carrier AirAsia Bhd.
Fanli, a Shanghai-based company, provides online discounts and sales. It currently has 70 million members, according to the company statement.