Since China was admitted to the World Trade Organization (WTO) on December 11, 2001, China has sped up its active participation in the competition of the world economy by lifting its trade and investment restrictions and limits. Its trading system is getting more and more free and its huge market with a population of 1.3 billion has been getting more and more open. With Chinas WTO accession, China has been honoring its commitments to its WTO members by complying with international business practices and WTO rules. For example, it will cut down its import tariffs for automobiles from the present 80% to 25% by 2006. Its financial sector and service industries are open to foreign investors now. As Chinas biggest business partner, Japan has benefited tremendously from Chinas open policies and deepening economic reform. In order to reduce the costs of production, a large number of enterprises from Japan have set up production bases in China since a Chinese workers wages accounts for only one tenth of those of a Japanese worker on the average. Japan has become one of Chinas biggest investors on a par with the United States of America (USA). How are the Japanese enterprises in Japan and in China adjusting themselves to the rapid changes of the Chinese market? What characteristics do the Japanese enterprises in China have? What effects has Chinas WTO accession had on those Japanese enterprises that have invested in China? This paper finds answers to the above questions. It at first reviews the Sino-Japanese economic and trade relations since 1980s, then analyses the situation and characteristics of Japanese-invested enterprises in China, and explores their problems in China. Finally it puts forward some suggestions for the Japanese enterprises in China.