Leijn Loevesijn (born 2 January 1949) is a former Dutch cyclist.

At the 1968 Summer Olympics Loevesijn, together with Jan Jansen won a silver medal in the 2000 metres tandem race, and finished fifth at the sprint race and sixth in the time trial. At the Track Cycling World Championships he won a bronze medal in the sprint in 1970 and a gold medal in the sprint in 1971. Between 1968 and 1976 he won 11 national titles in sprint disciplines.

After that he became a professional. In 1971 he was World Champion Sprint. He was the first Dutch World Champion since Jan Derksen in 1957, and it would take until 2004 before Theo Bos would succeed him. Loevesijn was eight times in row Dutch Champion sprint en won the "Grote Prijs van Amsterdam" three times.

He ended his career as a professional cyclist in 1976. Afterwards, he tried to combine his cycling activities with his work but in vain. Until his retirement in 2014 Leijn Loevesijn performed as a planning engineer with the water management and sewage services of the city of Amsterdam. Currently he is indirectly involved in cycling.