To obtain an additive composition useful for improving low- temperature fluid flow characteristic of fuel oil.

This additive composition comprises (i) an oil-soluble hydrogenated block diene polymer which is at least one kind of an oil-soluble hydrogenated block diene polymer comprising at least one crystalline block obtainable by tail to tail polymerization of a linear diene and at least one amorphous block, which is obtained by 1,2-configuration polymerization of a linear diene, polymerization of a branched diene or a combination of these polymerizations, (ii) at least one kind of an ethylenic unsaturated ester compound and (iii) at least one kind of comb polymer.