To provide a rubber processing oil having a polycyclic arom. compd. at a content of less than 3 wt.% which maintains a viscosity at the same level as that of the conventional oil, and is excellent in compatibility with an arom. type rubber, and to provide a rubber compsn. which does not cause bleeding of a vulcanized rubber compounded with the oil and is excellent in thermal aging properties.

This rubber processing oil has a polycyclic arom. compd. content of less than 3 wt.%, a dynamic viscosity at 100°C in the range of 20-32 mm2/s, a flash point (COC) of 230°C or more, a 5 vol.% distillation temp. of 370-530°C as well as an arom. compd. content by ASTM D 2007 (Clay-Gel analysis) of 25-35 wt.% and a polar compd. content of 15-20 wt.%. The rubber compsn. is obtd. by compounding a rubber with 10-25 wt.%, based on the whole rubber compsn. of the above rubber processing oil.