The union between Apple and UnionPay was announced late last year, but was subject to various approvals.
Shoppers around the world are being encouraged to use smartphones instead of cards to pay for in-store purchases.
Alibaba's Alipay currently dominates China's electronic payments market.
Apple confirmed its expansion into China on its website.
"You can now support Apple Pay for your customers in China, providing an easy, secure, and private way for them to pay using their China UnionPay credit and debit cards," the firm said.