We developed a transient photoinduced voltage measuring system and then investigated the photoinduced electron transfer in heterostructured polyimide Langmuir-Blodgett films consisting of a polyimide of one type (PI) and a polyimide of another type containing a tetraphenylporphyrin moiety (PORPI). The photoinduced transient voltage depended on the PORPI layers (n), indicating that there are two kinds of electron transfer mechanism. For n exceeding 3, the maximum value of the induced transient voltage increases with n. We conclude that photoexcited electrons were transported in PORPI films at a distance of 2-4 nm.