In this paper, electrical, optical and recombination losses in thin-film solar cells passed on CdS/CdTe have been evaluated. Electrical losses due to series and shunt resistances are quantitatively estimated from J-V curves. J-V characteristics are described in terms of the Sah– Noyce–Shockley theory of generation–recombination in the space-charge region of the CdS/CdTe heterostructure. Optical losses due to multiple reflections from the cell interfaces as well as absorption in the ITO and CdS layers are found using the refractive index and the extinction coefficient of the used materials. Losses arise from the recombination of the generated carriers at the front and rare surface of CdTe layer are carried out on the basis of the width of the space-charge region and other parameters of the absorber layer. It is found that the fill factor, output power density and the cell efficiency decreases with increasing the series resistance and decreasing the shunt resistance. The electrical losses due to series and shunt resistance are about 6%. Decreasing the thickness of window layer from 100 nm to 50 nm leads to increase the short-circuit current density from 23.6 mA/cm2 to 24.8 mA/cm2 and then reducing the optical losses from 24% to 20%. The recombination losses record a minimum value of 5% at width 1 μm of the space-charge region and record a maximum value of 27% at width=7μm.