The vapor‐liquid equilibrium of the hydrogen–n–butane system was studied at temperatures between 54° and 121°C and at pressures up to 167 atm. The fugacity of hydrogen in the vapor phase was measured directly by using a palladium‐silver semipermeable membrane, whereas p‐T‐x‐y data were obtained in a conventional manner.Henry's constants for hydrogen in n‐butane were obtained from the experimental fugacity data without making any assumptions about the vapor phase. Constant‐pressure, liquid‐phase activity coefficients for both hydrogen and n‐butane were calculated and correlated by using a modified van Laar equation.