Comparison of the effects of powder and ethanolic extract of the Red Kwao Kreur (~iButea superba~i Roxb.) from Wang Nam Khiao District Nakhon Rachasima Province and Sung Men District Phrae Province on the reproductive organs, reproductive behavior and erection in male albino rats were performed. The fertility of soil from these two areas were also studied. Two groups of the rats were given the powder and ethanolic extract of Red Kwao Kreur by using a gastric intubation at a dose of 0.25 , 0.5 and 5 mg./ml./time/day for 21 and 42 days, respectively. As for the 21 days of treatment, the result showed that the weight of the rats from the group given 0.25 mg./ml./time/day of powder and ethanolic extract of Red Kwao Kreur decreased significantly when compared with the control group. While the weight and the sperm count from the group given 0.5 and 5 mg./ml./time/day of powder increased significantly. Moreover, the ethanolic extract of 5 mg./ml./time/day also increased the relative weight of the seminal vesicle , prostate gland, and also the length of penis. After 42 days, the relative weight of seminal vesicles and the length of penis decreased. Furthermore, the two groups of rats showed the significant increase of libido and the size of penile erection. These result showed that the steroids and the flavonoid glycoside in the extraction of Red Kwao Kreur effected the testosterone and vasodilation cavernous vein. The soil from Sung Men District has more fertility than that from Wang Nam Khiao District.