Stock for a recoilless hunting rifle, for medium and large caliber hunting guns, which eliminates the stress produced by the effect of the recoil on the shooter's shoulder, providing at the same time good targeting precision and reduced consumption of bullet cartridges or shot cartridges. The stock has a stock butt and a mechanical anti-recoil module, with fast assembling, and a gun stock resembling the classical gun stocks but without transferring the recoil force to the shooter's shoulder. The recoilless buttstock includes a mechanical anti-recoil module, presented as an assembly having a pair of coupling parts, an elastic mechanism, a fixed support with rollers, an upper guide with a spring, a lower guide with a spring and the case of the stock.