Masato Uchishiba (内柴 正人, Uchishiba Masato?, born 17 June 1978 in Kōshi, Kumamoto) is a Japanese judoka who won the gold medal in the men's under 66 kg division at the 2004 Olympics in Athens, Greece and at the 2008 Olympics in Beijing, China. To win the Olympic gold at Athens, he defeated Jozef Krnáč of Slovakia. Of winning the gold, he said, "I wanted this so badly I wouldn't have cared if it was my last fight ever," though his comments were officially translated as: "It is probably my last Olympics, that is why I am proud of my medal." At the 2005 Judo World Championships, he won silver in his division. He also won the gold medal at the 2008 Summer Olympics against Benjamin Darbelet of France.
Starting in April 2010, Uchishiba coached the women's judo team at Kyushu University of Nursing and Social Welfare in Kumamoto Prefecture. In November 2011, the school released Uchishiba from his coaching position following sexual harassment allegations. On 6 December 2011, he was arrested by the Tokyo Metropolitan Police Department on suspicion of rape in Tokyo in September 2011. Uchishiba said that the act was consensual.