The incidence of infertility is increasing world wild. Among the diet factors, are the quality and quantity of the fat that contributes to spermatogenesis. Canola oil is known to contain oleic acid which is an omega-9 monounsaturated fatty acid, linoleic acid which is an essential omega-6 polyunsaturated fatty acid and alpha-linolenic acid, a plant-based omega-3. Canola oil has the lowest saturated fatty acid content among cooking oil. This study has been designed to investigate the possible effect of Canola oil, the recently used cooking oil, on the testicular structure and ultra-structure. Twelve adult male albino rats (200-250g) were obtained from the animal house in Faculty of Pharmacy, Mansoura University. The animals were housed two in a cage at a constant temperature of 18°C and humidity 45%. Rats were divided into control and treated; treated rats received a diet contains 7ml/100gm canola oil for 39 days. Six rats in each group were weighed and sacrificed at the end of the experiment; testis was dissected and weighed. The specimens were used for paraffin sections and electron microscope examination. The Canola oil-treated group showed irregular seminiferous tubules, germ cells with vacuolated cytoplasm and deeply stained nuclei compared with the control group. The treated testis ultrastructure showed degenerated Sertoli cell with an irregular nucleus, degenerated spermatocytes with the cytoplasm showing phagosomes, lysosomes and increased autophagic vacuoles. Interstitial cells appeared degenerated with vacuolated cytoplasm an. Canola oil is low in saturated fat and high in monounsaturated fat content,  making it an ideal healthy cooking oil. This study revealed that Canola oil usage resulted in distorted seminiferous tubules, degenerated germ cells and ultrastructural changes in the treated testis. Canola oil should be used with caution, especially in males, to avoid its hazardous effect on the testis.