Oral administration of aqueous extract of Calendula officinalis flower to male rats at the dose level of 100mg/kg body weight for 60 days did not cause body weight loss but decreased the weight of testis, epididymis, seminal vesicle and ventral prostate in a significant manner. Sperm motility as well as sperm density were reduced highly significantly which resulted in 45% negative fertility. Serum testosterone level showed highly significant reduction. Biochemical parameters like total protein and Sialic acid in testis, epididymis, seminal vesicles and ventral prostate were decreased significantly where as testicular cholesterol concentration was elevated. All the haematological parameters were in normal range when compared with the control group animals. It is concluded that oral administration of aqueous extract of C. officinalis (Plant) showed a significant effect on fertility in male rats without interfering general physiology of rats.