The study provides a number of observations regarding effects of methanol extract and its fraction (Fraction-B) of leaf of Aegle marmelos (family Rutaceae) on infertility in male albino rats, in determination of its mean lethal dose and its dosage form as microcapsules. Dose dependent response of methanol extract and Fraction-B of A.marmelos leaf were noted on in vitro motility of human spermatozoa. The in vivo antifertility activity of Fraction-B has been done in male albino rats. The anabolic effect suggested that Fraction-B has no general toxic effect on body growth. The weight of testis, epididymis and prostate gland was decreased, but the weight of seminal vesicle increased significantly in treated group. The histological study showed the blood supply around the seminiferous tubules was increased which was interpreted on the basis of dilated blood vessels. While in case of control group the blood supply was normal, Leydig's cells were showing hypertrophy in case of treated group. Sertoli cells were highly proliferated with large number of immature sperms adhere to them in Fraction-B treated group. The sperm motility and morphology showed increase in the number of morphological