The kinetics of stead!, dynamic Wetting of a liquid replacing a gas saturated,vith the liquid vapor on smooth solid surface in horizontal capillary tubes is investigated theoretically and experimentally, An approximate analytical method for advancing the dynamic meniscus of the liquids is proposed, and the effects of liquid now, equilibrium contact angle, and adsorbed layer thickness at the gas-solid interface are studied, The analytical results show that dynamic netting depends on liquid now near the contact line, and the effect of the liquid now far from there is insignificant. Furthermore, it is found that the dynamic contact angle is a function of not only capillary number, but also equilibrium contact angle, and adsorbed layer thickness. Experiments were carried out on dynamic wetting of hexane, octane and butanol in polytetrafluoroethylene tubes. The experimental data of dynamic contact angle in the present and previous studies are in fairly good agreement with the theoretical predictions over wide ranges of capillary numbers and equilibrium contact angles.