Wikipedia
OKCoin
OKCoin is the largest Bitcoin company in China with core product lines of a Bitcoin exchange, and a mobile consumer payment and lending app. OKCoin operates the largest Bitcoin exchange and through blockchain technology, seeks to dramatically improve payment systems. OKCoin Exchange China operates CNY/BTC spot pair with margin trading from its Beijing entity, while OKCoin International operates USD/BTC spot pair with margin trading and BTC/USD futures from its Singapore entity.
As of August 2016, OKCoin is the largest Bitcoin exchange in the world with a volume of over 16,000,000 Bitcoins per month.