Experimental data are presented for the void fraction and the shear stresses of stratified gas-liquid Row in a pipe. A new technique was used to measure the interface shear stress. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress profile at the gas-liquid interface. A new formula, relating to the interfacial friction factor with the void fraction and superficial gas Reynold number, was developed to predict the interface shear stress. The predicted values are in good agreement with experimental data.