Fungicides are toxic chemicals, very much used in agriculture, but they are associated with the appearance of certain metabolic, carcinogenic, neurotoxic and fertility disorders. The objective of this work is to study the toxic effect of the dithiocarbamate “thiram 80% purity” on seasonal reproduction of male domestic pigeons Columba livia domestica, subjected to a long photoperiod (19L: 05D). The fungicide was orally administered at 5 and 10 mg/Kg body weight/day for 10 consecutive weeks.Testicular volume and weights were measured weekly, whereas semen quality, and histopathological profile were investigated at week 10.The obtained results reveal that under a long photoperiodthe sexual activity of the control lasted only 04 weeks, characterized by significant increase in the testicular volume, followed by spontaneous gonadal regressionup to week 10. Consequently, an azospermia and lack of germ cells in control birds was noticed,which confirm the testicular regression.In the treated groups, thiram delayed the refractory phase along the experimental period, but testicular weight were superior in the treated pigeons compared to the control during the last weeks. Treated pigeons had more dead spermatozoa compared to the control. Remarkably, abnormal spermatozoa were much higher in the group received 5mg than that of 10mg.The histological profile revealed degenerative changes in testes of treated pigeons with elongated and irregular diameter of seminiferous tubules, degenerative of Sertoli cells, severe atrophy of Leydig cells and pronounced decrease in the interstitial space. However, in the treated groups the stages of spermatogenesis appear unaffected, accompanied withimmature and malformed spermatozoa in the lumen.To conclude, oral administration of thiram may affect the seasonal reproduction of pigeon by disturbing the histo-architecture of testes and sperm quality under long photoperiod. Such changes may be responsible for delayed refractory phase.The intact stages of spermatogenesis indicates that the thiram-exposed pigeons were not in the refractoriness period.