To obtain a rubber composition improved in low heat buildup properties while maintaining the modulus and a pneumatic tire using the rubber composition.

This rubber composition comprises a 12-18C saturated fatty acid which is a solid at normal temperature in an amount of 0.5-15 pts.wt. based on 100 pts.wt. of a rubber containing ≥50 wt.% of a natural rubber, an 18C unsaturated fatty acid that is a liquid at normal temperature in an amount of 0.5-15 pts.wt. based on 100 pts.wt. of the rubber containing ≥50 wt.% of the natural rubber and a carbon black having ≥100 m2/g nitrogen adsorption specific surface area (N2SA) in an amount of 30-100 pts.wt. based on 100 pt.wt. of the rubber containing ≥50 wt.% of the natural rubber in ≤2 weight ratio of the saturated fatty acid to the unsaturated fatty acid expressed in terms of the saturated fatty acid/unsaturated fatty acid. The pneumatic tire uses the rubber composition in a tread.