The effect of quenching and tempering structure of various carbon steels on the diffusivity and solubility of hydrogen were studied at room temperature by using an electrochemical permeation technique. The minimum diffusion coefficient is obtained when the steels are in the as-quenched state; i.e, in a martensitic structure the diffusion coefficient increases with increasing tempering temperature. On the other hand, the solubility of hydrogen is a maximum for the quenched martensitic structure and decreases with increasing tempering temperature. An increase in carbon content reduces the diffusivity but increases the solubility of hydrogen. The variations in diffusivity and solubility can be explained in terms of hydrogen trapping process involving lattice imperfections such as dislocations, lattice vacancies and subgrain boundaries, etc, produced by martensitic transformation.