Transient photocurrents in amorphous selenium (a‐Se) and nematic liquid crystal (NLC) double layers have been investigated to elucidate the charge carrier transport process in NLC. It is shown that the transient photocurrents obtained in the experiment are space‐charge limited currents induced by the delayed charge injection from thea‐Se layer to the NLC layer. The mobile charge carriers are found to be positive ions with the drift mobility of 3.5×10−6cm2/V s at 303 K and the ionic radius of 0.32 nm in 4‐cyano‐4′‐alkyl‐biphenyl. The origin of the ions is briefly discussed. ©1995 American Institute of Physics.