Polymer composition, lubricating oil additive composition, and lubricating oil composition

A polymer composition comprising a comb-shaped polymer (X) comprising the following structural units (a) to (c), and a hetero atom-comprising base oil (Y),

• the structural unit (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,
• the structural unit (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
• the structural unit (c):
• a structural unit derived from a macromonomer (C),
• wherein
• a content of the structural unit (a) is 70% by mass or more based on a total of the structural units of the comb-shaped polymer (X), and
• the hetero atom-comprising base oil (Y) has a kinematic viscosity at 40° C. of 25 mm2/s or less.