Koji Alexander Murofushi (Japanese: 室伏 アレクサンダー 広治, Murofushi Arekusandā Kōji; born October 8, 1974 in Numazu, Shizuoka) is a Japanese hammer thrower. He has been among the world elite since the 2001 World Championships in Athletics, where he won the silver medal.
He proceeded by winning the 2002 Asian Championships and Asian Games as well as a bronze medal at the 2003 World Championships. That year he threw 84.86 metres, which was the longest hammer throw in over ten years, putting Murofushi 5th on the all-time performer's list. Among the favorites at the 2004 Summer Olympics, he eventually won the gold medal after the disqualification of Adrian Annus.
Murofushi comes from a hammer throwing family, as his father Shigenobu Murofushi is a former Olympian and held the Japanese record for decades, and his sister, Yuka Murofushi, also throws hammer as well as discus. Murofushi's mother, Serafina Moritz, was a javelin thrower representing Romania.