Novel second harmonic generation (SHG) was observed from the crystalline powder of the ion-pair charge-transfer (CT) complexes consisting of 1-methyl-4-(4-nitrostyryl)pyridinium as an acceptor and tetraphenylborate as a donor. The second harmonic light intensity dramatically decreased upon excitation of a CT band due to the photoinduced electron transfer from tetraphenylborate to styrylpyridinium moiety. These results strongly suggested that the CT transition in the ion-pair complexes would cause SHG. The crystalline structure of an ion-pair CT complex of 1-methyl-4-(4-cyanostyryl)pyridinium tetraphenylborate which also exhibited strong SHG was investigated to elucidate the mechanism of the SHG in the ion-pair CT complex system.