The authors report the characteristics of organic solar cells (OSCs) fabricated on HNO3-treated multilayer graphene (MLG) transparent electrodes. MLG transparent electrodes were prepared using chemical vapor deposition and a multitransfer process. Compared to untreated-MLG electrodes with a fairly high sheet resistance (274 ± 1 Ω/sq) even though three layers of graphene were stacked together, HNO3-treated MLG electrode shows a lower sheet resistance of 119 ± 1 Ω/sq. OSCs (MLG/poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Poly(3-hexylthiophere)/1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61/Ca/Al) fabricated on untreated-MLG transparent electrodes had an open-circuit voltage of 0.575 V, a short-circuit current of 8.08 mA/cm2, a fill factor of 43.5%, and a power conversion efficiency (PCE) of 2.02%. In contrast, application of HNO3-treated MLG films as transparent electrodes for OSCs led to improved performance with an open-circuit voltage of 0.602 V, a short-circuit current of 8.26 mA/cm2, a fill factor of 57.5%, and a PCE of 2.86%. These results suggest that HNO3 treatment is a promising method for improving the performance of large-area OSCs based on MLG electrodes.