A polymer composition contains a comb-shaped polymer (X) containing the following structural units (a) to (c): (a): a structural unit derived from a short-chain alkyl (meth)acrylate (A) having a short-chain alkyl group having 1 to 5 carbon atoms; (b): a structural unit derived from a long-chain alkyl (meth)acrylate (B) having a long-chain alkyl group having 6 to 32 carbon atoms; and (c): a structural unit derived from a macromonomer (C), a content of the structural unit (a) being 70% by mass or more based on the total structural units of the comb-shaped polymer (X); and a hetero atom-containing base oil (Y). The hetero atom-containing base oil (Y) has a kinematic viscosity at 40° C. of 25 mm2/s or less.