On the campaign trail, Mitt Romney has become increasingly critical of China, saying the country is engaging in unfair trade practices and vowing to crack down on them in ways that are much more severe that the current administration.

The 2011 tax returns his campaign released on Friday show that Mr. Romney’s family trusts had invested in shares of a Chinese-owned state oil company but got rid of those investments this summer as Mr. Romney’s anti-Chinese rhetoric heated up on the campaign trail.

In 2009 and 2010, the W. Mitt Romney blind trust invested $77,262 in shares of Cnooc Limited, the state-owned Chinese oil company, and Industrial and Commercial Bank of China. On Aug. 10, 2011, as Mr. Romney was emerging as a harsh critic of China, the shares were sold, producing a profit of $8,138, as the trust made money on the oil company but lost money on the bank.

The trust also invested in derivative securities linked to the Japanese stock market and to an index that includes stocks in every major country except the United States. It invested in a derivative that would profit if the dollar fell against a group of foreign currencies.

Mr. Romney’s campaign has repeatedly criticized President Obama for failing to take a tough line against Chinese trade practices. After Mr. Obama this week announced tough new trade actions against China, Mr. Romney took credit for forcing the president’s hand.

“President Obama has spent 43 months failing to confront China’s unfair trade practices,” Mr. Romney said in a statement after Mr. Obama’s announced that the government had filed trade complaints against China. “Campaign-season trade cases may sound good on the stump, but it is too little, too late for American businesses and middle-class families.

The Romney family trusts invested around the world. It also owned shares in Credit Suisse, the Swiss bank; FLSmidth, a Danish machinery company; Arcelormittal, a steel company based in Luxembourg with operations around the world, and Komatsu, a Japanese machinery company. All those investments were sold on Aug. 10, the day before a Republican debate in Iowa.