Jun O'Hara, legally named , is a Japanese mathematician who works on the fields of low-dimensional topology and knot theory. He is a professor at Chiba University.
He is famous for his discovery of Möbius energy, a type of knot energy.
He was born on 29 March 1963 in Hiroshima, Japan.
He was a PhD student of Takashi Tsuboi at the University of Tokyo.