Wistar nonlinear rats weighing 170-220g. Rats were divided 5 groups, including control group, group-1, group-2, group -3 and reference group. Dried thistle extract and raw bovine testicle were contained by 1:1, 1:2 and 2:1 ratio. Each 0.1g ratio was dissolved in 20 ml distilled water and administered 2 times per day. Blood sampling was done for each rat after 3, 7, 14, 21, 28 and 35 days. Their testosterone level was measured by ELISA Kit. Results: The results indicated that free serum testosterone level in male rats increase and decrease in 7 days frequency. All tested groups showed gradual increase in the level of free serum testosterone when compared to that of corresponding control (p<0.05). Statistical comparison of all groups revealed that the maximum level was found in group 1. Moreover, group 3 was showed gradually increase in level of free serum testosterone, irrelative with period of decrease testosterone level. Conclusion: According to our results and previous study, it is suggested that preparation with Tribulus terrestris L. extract could be used in the androgen deficiency and erectile dysfunctions. Keywords: Tribulus Terrestris L, Free testosterone, Dihydrotestosterone, Protodioscin