The microstructure-dependence of photoelectric properties have been studied for Langmuir-Blodgett (LB) films containing 5-(4-N-decylpyridinium)-10, 15, 20-tri-p-tolyl porphyrin (PyP) and arachidic acid (AA). Two-dimensional distribution profiles of short-circuit photocurrent (Isc) exhibited clear bumps and valleys for the LB films with large PyP or AA domains. The spatial averages of Isc tended to show lower values for smaller domain structures, suggesting a great contribution of carrier recombination at the PyP-AA interface.