A silicone rubber composition comprising (A) an organopolysiloxane composition of the organic peroxide cure or addition reaction cure type, (B) a normally solid organic compound having at least two ester bonds per molecule, and (C) particulate aluminum hydroxide having an average particle size of up to 20 μm is suited for use as high-voltage electric insulator since it maintains insulating properties for a long term in outdoor service and has acid resistance and a long lifetime even in polluted areas.