Photocurrent generation of porphyrin-terminated helical peptide self-assembled monolayers (SAMs) was studied in an aqueous solution. The anodic photocurrent was prevailing, but the cathodic photocurrent was observed with applying negative bias voltage on the working electrode. The bias dependence of the photocurrent was explained successfully by theoretical calculation with taking into account the redox potential shift by J-aggregate of porpyrins, the helix dipole, and photoenergy migration in the SAM. The dark current was insignificant even at the forward bias voltage.