γ-Hexachlorocyclohexane (γ-HCH) is a man-made chlorinated insecticide that has caused serious environmental problems. Here, we report the complete genome sequence of the γ-HCH-degrading bacterium Sphingomonas sp. strain MM-1, which consists of one chromosome and five plasmids. All the specific lin genes that are almost identical to those of Sphingobium japonicum UT26 for the conversion of γ-HCH to β-ketoadipate are dispersed on four out of the five plasmids.