PURPOSE: To obtain a composition for a refrigerating machine hydraulic fluid having excellent electrical insulating properties, moisture absorption, compatibility and thermal stability by blending a refrigerating machine oil comprising a specific ester as a base oil with a hydrofluorocarbon.

CONSTITUTION: A refrigerating machine oil comprising an ester which is selected from (A) an ester obtained from (i) an aliphatic polyhydric alcohol containing 1-6 primary hydroxyl groups and (ii) a 2-9C straight-chain or branched saturated aliphatic monocarboxylic acid (derivative), (B) an ester obtained from the components (i) and (ii) and (iii) a 2-10C straight-chain or branched saturated aliphatic dicarboxylic acid (derivative) and (C) an ester obtained from the component (i), (iv) a 1-10C straight-chain or branched saturated aliphatic monohydric alcohol and (v) a 2-10C polyfunctional carboxylic acid or its derivative and has ≤1 Ig/100g iodine value is blended with a hydrofluorocarbon to give the objective composition.