An experimental investigaiton into an air-water two-phase annular flow in a horizontal tube and near horizontal tubes was carried out. The inclination angles of the tube to horizontal were -10^°, 0^°, 10^° and 15^°, where minus means the downward flow. Tube diameter was 26.0 mm. Volumetric fluxes of air and water ranged from 10 m/s to 50 m/s and from 0.002 m/s to 0.4 m/s, respectively. Hold-up, frictional pressure drop and the circumferential position from which liquid film starts to form were measured and the effect of the tube inclination on these parameters were examined. As the results, it was made clear that the effects of tube inclination could not be neglected even in the case of slight inclination and that the mean film thickness averaged over the circumference of the tube was approximately equal to the local mean film thickness at θ= 120^° independent of the inclination.