The present invention provides a rubber composition for a breaker, which achieves both good fuel economy and good breaking performance while simultaneously having excellent processability, and a pneumatic tire including a breaker produced using the rubber composition. The present invention relates to a rubber composition for a breaker, including: a rubber component that contains a modified natural rubber, the rubber having a phosphorus content of 200 ppm or less; and carbon black and/or a white filler, wherein the rubber composition contains 5% by mass or more of the modified natural rubber based on 100% by mass of the rubber component.