The relationship between average grain size on the surface of SnO2transparent conductive film and conversion efficiency of the a-Si:H solar cell was investigated. a-Si:H solar cells were fabricated on SnO2/glass substrates with various grain sizes. The cell structure was glass/p(SiC)-i-n/Al and the effective cell area was 4 × 10-2cm2. The reflectivity from the glass substrate was reduced to about 7 percent with increasing the grain size from 0.1 to 0.8µm, and the short-circuit current was inceased from 12 to 14mA/cm2. A 7.9 percent of conversion efficiency was achieved using milky SnO2film of 0.4-µm average grain size at AM-100mW/cm2.