Summary:The aim of this study was to determine the effects of the testosterone hormone level on morphometry and vascular endothelial growth factor (VEGF) expression level of thoracic aorta of aged mice using histological and molecular techniques. A total of 30 aged mice (15 males and 15 females) were enrolled in 3 study groups: sham operation group (Control), gonadectomy group (G) and gonadectomy and testosterone supplementation group (GTS). Serum testosterone levels were measured by ELISA. Intima and media thickness and inner diameter of thoracic aorta were measured by morphometric investigation. The levels of the angiogenic factor, VEGF (vascular endothelial growth factor) mRNA in thoracic aorta were determined by RT-PCR. Although the alterations in the level of testosterone had no significant effects on intima or media thickness of the male thoracic aorta, in female, there was a significant increase (p<0.01) on intimal thickness in thoracic aorta following gonadectomy and hormone supplementation. The largest inner diameter was in testosterone supplementation groups of both sexes. Gonadectomie operation caused decrease in VEGF mRNA levels of thoracic aorta in male (p<0.05) and female mice. Interestingly, testosterone replacement caused an important decrease (p<0.01) in the expression of VEGF of aorta in female whereas resulted with an increase in male. Present results showed that testosterone hormone had different angiogenic effects on thoracic aorta in male and female aged mice. Additionally, gonadectomie operation in aged mice caused decrease in the level of VEGF mRNA levels in both sexes.