Nitric oxide (NO) a gaseous neurotransmitter is reported to play an important role in controlling the release of luteinizing hormone releasing hormone (LHRH) in mammalian system. But its role has not been investigated in birds, where photoperiod plays an important role in regulating gonadal development. To investigate the effect of NO on gonadal and adrenal function of Japanese quail, in the first experiment, 3-weeks-old sexually immature quail received NO donor sodium nitroprusside (SNP, 5mg/100g body weight) orally or nitric oxide synthase (NOS) inhibitor N-nitro L-arginine methyl ester (L-NAME, 25 microg/100g body weight) intraperitoneally for 13 days in continuous condition of light (LL). Thereafter treated quail along with their respective controls were shifted to long day length (LD 16:8) for 21 days when the study was terminated. Results indicate that SNP treatment stimulated and L-NAME suppressed body weight, cloacal gland volume (an androgen dependent sex accessory organ), testes (gonado-somatic index, spermatogenesis), epididymis (histology) and adrenal (weight, histology, cortico-medullary ratio) function as well as total nitrite and nitrate concentration in plasma, hypothalamus and testes. In the second experiment, two groups of 3-weeks-old birds were maintained in short day length (LD 6:18) or long day length (LD 16:8) for 5 weeks to induce gonadal suppression and stimulation, respectively. Thereafter birds of both the photoperiod were divided into two subgroups, the short day quail receiving normal saline (SD Con) or SNP (SD+SNP) while long day quail received normal saline (LD Con) or L-NAME (LD+L-NAME) for 13 days and were maintained in their respective photoperiods, until the termination of study (21 days post treatment period). SNP stimulated all the parameters even in short day condition and L-NAME suppressed in long day quail compared to their respective controls. These findings indicate positive control of NO on the gonad and adrenal function of Japanese quail which exhibits parallel adrenal-gonad relationship. Further, NO donor induces long day effects while NOS inhibitor mimics short day effects. It is concluded that NO may not only regulate hypothalamo-hypophyseal-gonadal and -adrenal axis of Japanese quail but may also modulate its photosexual responses.