China–Japan relations or Sino–Japanese relations (simplified Chinese: 中日关系; traditional Chinese: 中日關係; pinyin: Zhōngrì guānxì; Japanese: 日中関係, romanized: Nicchū kankei) are the bilateral relations between China and Japan. The countries are geographically separated by the East China Sea. Japan has been strongly influenced throughout its history by China, especially by the East and Southeast through the gradual process of Sinicization with its language, architecture, culture, cuisine, religion, philosophy, and law. When Japan was forced to open trade relations with the West after the Perry Expedition in the mid-19th century, Japan plunged itself through an active process of Westernization during the Meiji Restoration in 1868 and began viewing China under the Qing Dynasty as an antiquated civilization; unable to defend itself against foreign forces in part due to the First and Second Opium Wars along with the Eight-Nation Alliance's involvement in suppressing the Boxer Rebellion. Japan eventually took advantage of such weaknesses by invading China, including the First Sino-Japanese War and the Second Sino-Japanese War.

According to the Chinese government, the relationship between China and Japan has been strained at times by Japan's refusal to acknowledge its wartime crimes to the satisfaction of China. However, according to the Japanese government, it stated that the expansion of the People's Liberation Army and its assertive actions are the cause of such strained relations. Revisionist comments and visits to the Yasukuni Shirne by prominent Japanese officials and some Japanese history textbooks regarding the 1937 Nanking massacre have been a focus of particular controversy. Sino-Japanese relations warmed considerably after Shinzō Abe became the Prime Minister of Japan in September 2006, and a joint historical study conducted by China and Japan released a report in 2010 which pointed toward a new consensus on the issue of Japanese war crimes. The Senkaku Islands dispute also resulted in a number of hostile encounters in the East China Sea, heated rhetoric, and protests in China and Taiwan.China's and Japan's economies are respectively the world's second and third-largest economies by nominal GDP. Also, China's and Japan's economies are the world's first and fourth-largest economies by GDP PPP. In 2008, China-Japan trade grew to $266.4 billion, a rise of 12.5 percent on 2007, making China and Japan the top two-way trading partners. China was also the biggest destination for Japanese exports in 2009. Since the end of World War II, Sino-Japanese relations are still mired with geopolitical disagreements. The enmity between these two countries emanated from the history of the Japanese war and the imperialism and maritime disputes in the East China Sea. Thus, as much as these two nations are close business partners, there is an undercurrent of tension, which the leaders from both sides are trying to quell. Chinese and Japanese leaders have met several times face to face to try to build a cordial relationship between the two countries.Despite the disagreements, China and Japan have been steadily improving their relationships, with both sides remarking that they will be focusing on developing healthy ties, signalling towards a "new start". Both countries have started to cooperate in numerous areas, including boosting global trade and Asia's economic activities, working hand-in-hand on One Belt One Road Initiative, setting up maritime and air contact system for better communication, as well as holding several high level meetings and consultations. In 2018, the two countries pledged to further deepen ties and shares a common ground on the trade war, with Shinzō Abe saying that "Japan–China relations have been moving in the direction of great improvement". In 2022, China and Japan commemorated the 50th anniversary of the normalization of relations between their two nations.