Experiments were carried out to examine the characteristics of the vapor-liquid two-phase pressure drop of a refrigerant R 410A flowing in horizontal copper circular and rectangular tubes, and their hydraulic diameters were 1.00 and 1.02 mm, respectively. Pressure drops were measured at mass velocities from 30 to 400 kg/(m2·s) and qualities from 0.05 to 0.9, and the saturation temperature of 10 °C under the adiabatic condition. Based on the observations of vapor-liquid two-phase flow patterns and the comparison with the data for vertically upward and downward flow in the circular and rectangular tubes previously obtained, the effects of the cross-sectional shape and flow direction on the characteristic of pressure drop were clarified. In addition, the measured pressure drops were compared with the existing correlations and their applicability were examined.