Sebastolobus macrochir, the broadbanded thornyhead or broadfin thorny head, is a species of marine ray-finned fish belonging to the subfamily Sebastinae, the rockfishes, part of the family Scorpaenidae.

Sebastolobus macrochir was first formally described in 1877 as Sebastes macrochir by the German born British ichthyologist and herpetologist Albert Günther with the type locality given as the Inland Sea of Japan.

[3][2] The specific name acrochir is a compound of macro which means "long" or "large" and cheirus meaning "hand", an allusion to the broad pectoral fin with its upper 5 or 6 tays elongatedrays.

[5] Its range extends from Sagami Bay in Japan north to the Kuril Islands and Sakhalin in Russia.

[1] Sebastolobus macrochir is found in areas where there is steep bottom relief near areas of very deep water which results in turbulent currents rising vertically from deeper water, bringing food items to the fish.