A rubber composition for an inner liner improving air retention property of a tire, lowering hysteresis loss and further preventing crack growth is provided. A rubber composition for an inner liner comprising 10 to 50 parts by weight of mica having an aspect ratio of at least 50 and an average particle diameter of 40 to 100 .mu.m, based on 100 parts by weight of a rubber component comprising 30 to 60% by weight of butyl base rubber, 20 to 50% by weight of natural rubber or isoprene rubber and 10 to 40% by weight of butadiene rubber.