HYDRAULIC OIL COMPOSITION

摘要

PROBLEM TO BE SOLVED: To provide a hydraulic oil composition capable of securing both of prevention of inner leakage and reduction of piping resistance and improving energy efficiency of whole hydraulic system.SOLUTION: There is provided a hydraulic oil composition containing a lubricant base oil having a kinetic viscosity at 40°C of 15 to 50 mm/s and polymethacrylate having a number average molecular weight of 48000 or less of 1 to 40 mass% based on total amount of the composition, and having a viscosity index of 150 or more and a ratio of (A) kinetic viscosity (unit:mm/s) and (B) shear viscosity (unit:mPa s, shear condition:10/s) (A/B) of 1.3 or less at 60 to 80°C.