The present invention provides a 1,3,7-octatriene polymer having a narrow molecular weight distribution and a hydride thereof. Specifically, the 1,3,7-octatriene polymer is a polymer containing a structural unit derived from 1,3,7-octatriene, wherein the polymer has not only a molecular weight distribution (Mw/Mn) of 2.05 or less but also a weight average molecular weight (Mw) of 1,000 to 1,000,000.