The funds stood at 21.5278 trillion yuan (about 3.15 trillion U.S. dollars) at the end of August, down from 21.5302 trillion yuan a month earlier, ending a seven-month gaining streak, according to the People's Bank of China.
As Chinese currency is not freely convertible under the capital account, the central bank has to purchase foreign currency generated by trade surplus and foreign investment in the country, adding funds to the money market.
Such funds are an important indicator of cross-border foreign capital flows and domestic yuan liquidity.
As a similar measure of capital flows, China's foreign exchange reserves stood at 3.1097 trillion U.S. dollars in August, down 0.26 percent from a month ago.
The State Administration of Foreign Exchange said China's cross-border capital flows were still at a balanced level despite external factors including trade frictions and an upward U.S. dollar index that contributed to the falling reserves.