AIM: Smallanthus sonchifolius (Yacon) has been used as a food and folk medicine in the Andes region. It was screened the pharmacological effects of a 50% ethanol extract of Yacon on spermatogenesis in rats. This study is carried out to evaluate the possibility of using Yacon tubers extracts as a fertility agent to treat infertility caused by spermatogenic disorders. METHODS: The dried, pulverized Yacon tubers were extracted with 50% ethanol at 50 ℃ for 5 h under sonication. The Yacon extracts were analyzed by using HPLC system on a Kromasil C18 column (250 mm×4.6 mm). The Yacon tubers extracts, chlorogenic acid and ferulic acid were administrated to rats once daily by oral gavage. The number of sperm heads in the testis was assessed by counting the number of sperm heads using slight modification of the procedure reported by Toth et al (1989). RESULTS: After administration of chlorogenic acid and Yacon tuber extracts to rat for 5 weeks, the number of sperm in epididymis were increased by 20.33% and 34.48%, respectively. The ferulic acid which was reported as a metabolite of chlorogenic acid and constituent of Yacon to estimate the spermatogenic activity was also administered. After administration of ferulic acid and Yacon tubers extracts, the sperm number were increased by 37.87% and 43.33%, respectively. Spermatogenic effects of chlorogenic acid and ferulic acid were 0.59 times and 0.87 times of Yacon tubers extracts, respectively. CONCLUSION: The spermatogenic effect of Yacon tubers extracts may result from the combined effect of chlorogenic acid or its analogues and their metabolites. AIM: Smallanthus sonchifolius (Yacon) has been used as a food and folk medicine in the Andes region. It was screened the pharmacological effects of a 50% ethanol extract of Yacon on spermatogenesis in rats. This study is carried out to evaluate the possibility of The used Yacon tubers extracts as a fertility agent to treat infertility caused by spermatogenic disorders. METHODS: The dried, pulverized Yacon tubers were extracted with 50% ethanol at 50 °C for 5 h under sonication. The Yacon extracts were analyzed by using HPLC system on a Kromasil C18 column (250 mm×4.6 mm). The number of sperms in the testis was assessed by counting the number of sperm heads using slight. Modification of the procedure reported by Toth et al (1989). RESULTS: After administration of chlorogenic acid and Yacon tuber extracts to rat for 5 weeks, the number of sperm in epididymis were increased d by 20.33% and 34.48%, respectively. The ferulic acid which was reported as a metabolite of chlorogenic acid and constituent of Yacon to estimate the spermatogenic activity was also administered. After administration of ferulic acid and Yacon tubers extracts, the sperm number were increased By 37.87% and 43.33%, respectively. Spermatogenic effects of chlorogenic acid and ferulic acid were 0.59 times and 0.87 times of Yacon tubers extracts, may. CONCLUSION: The spermatogenic effect of Yacon tubers extracts may result from the combined effect of chlorogenic acid or its Analogues and their metabolites.