This paper deals with an experimental investigation of two-phase frictional pressure drop behavior of 1,1-difluoroethane in an 8 mm inside-diameter smooth horizontal tube. Pressure drop characteristics are measured in a pressure range of 0.19—0.41 MPa, heat flux range of 14—62 kW/m2, and mass flux range of 128—200 kg/m2s. The effects of experimental parameters on pressure drop are analyzed. It is found that with the increases of mass flow and vapor quality, the frictional pressure drop increases. The proportion of momentum pressure drop in the total pressure drop increases slightly as heat flux increases, and accordingly the proportion of the frictional pressure drop decreases. The frictional pressure drop increases with saturation pressure decreasing. Experimental results are compared with the calculations from the two extensively used correlation formulae. Our investigations show that the Friedel model has a relatively large deviation, and the Müller-Steinhagen-Heck model accords well with the experimental results.