The photoelectrochemical behavior of poly(N-methylpyrrole) in strong magnetic fields was investigated. When the magnetic field was increased from 0 to 3, then to 7 T, the intensity of the initial photocurrent of the poly(N-methylpyrrole) (PPy) modified electrode was increased in 0. 1 M NaClO4 + acetonitrile solution. When dichloromethane solution containing BU4NClO4 was used as an electrolyte, the dependence of the photocurrent on the magnetic field was also observed not only in the initial but in the second and third photocurrent responses. Interestingly, the photocurrent of the PPy modified electrode increased not only with the magnetic field, but also by each repetition of measurement. In repetitive measurements of the photocurrent strong magnetic fields obviously accelerated the increasing photocurrent compared with that in a zero magnetic field. Thus, the photocurrent of a conducting polymer-modified electrode can be controlled by a strong magnetic field. This is the first example of a magnetic field effect on the photo electrochemistry of a conducting polymer.