Modified electrodes were prepared by depositing a monolayer containing porphyrin-viologen linked compounds with various spacer chain-length on ITO electrodes by Langmuir-Blodgett method. Stable anodic photocurrents were observed by visible light irradiation upon the modified electrodes. The photocurrents were clearly enhanced in the presence of magnetic fields. Effects of spacer chain-length on the magnetic field effects are caused by photoactive triplet radical pairs.