To obtain an additive concentrate, capable of imparting excellent low-temperature characteristics and improving properties of viscosity index and useful as a viscosity improver, etc., by including a specific organic diluent and a specified ester in a specific proportion therein.

This additive concentrate comprises (A) 5-95wt.% organic diluent such as a naphthenic oil or a synthetic oil and (B) 95-5wt.% ester derived from a carboxy-containing interpolymer having 0.05-0.35 reduced specific viscosity. The interpolymer is derived from two or more monomers of components (i) and (ii). (i) either one of the monomers is one or more of a 2-30C aliphatic olefin and a vinyl aromatic monomer and (ii) the other of the monomers is one or more α,β-unsaturated acylating agents. The ester has 20-70mol% of 12-19C ester groups (based on the number of mol of carboxyl groups in the interpolymer) and 80-30mol% of 8-11C ester groups (based on the number of mol of the carboxyl groups in the interpolymer), derived from carboxy groups of the interpolymer and present in the polymeric structure thereof.