Nobuo Sekine (関根伸夫, Sekine Nobuo; September 19, 1942 – May 13, 2019), was a Japanese sculptor. He was one of the key members of Mono-ha, a group of artists who became known in the late 1960s and 1970s. He was born in Saitama, Japan. In October 1968, he created his best known work "Phase: Mother Earth" in Kobe’s Suma Rikyu Park for the "First Open Air Contemporary Sculpture Exhibition" (第一回野外彫刻展).