Objective: To investigate the impact of ethanol extract of Spondias(S.) mombin leaves on the biochemical parameters of testicular function, hormonal profile, sperm profile and reproductive outcomes of guinea pigs. Methods: Sexually matured male [(1000.40±8.12) g] and female [(810.00±7.09) g] guinea pigs were used. In testicular function study, a total of 24 male guinea pigs were randomised into 4 groups of 6 guinea pigs each. Group A (control) was orally administered 1 mL of physiological saline, once daily for 60 days while groups B, C and D were treated like the control group except that they were orally administered 100, 250 and 500 mg/kg body weight of ethanol extract of S. mombin leaves. For the fertility study, the same animal groupings and treatments in the testicular function study were adopted. The male guinea pigs were paired with the females (1:1) and afterwards examined for pregnancy outcomes. Results: The ethanol extract of S. mombin leaves contained saponins, alkaloids, flavonoids, tannins, steroids, phenolics, phlobatannins, cardiac glycosides, cardenolides and dienolides with saponins (4.80 mg/mL) occurring the most whilst cardenolides and dienolides (0.08 mg/mL) were the least. The ethanol extract of S. mombin leaves significantly and dose dependently reduced the activities of alkaline phosphatase, glutamate dehydrogenase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, malic enzyme, 17-β-hydroxysteroid dehydrogenase, lactate dehydrogenase, catalase and superoxide dismutase as well as levels of testosterone, glycogen, total protein and ascorbic acid in the testes when compared with the control group (P<0.05). All the doses of ethanol extract of S. mombin leaves also reduced the levels of sorbitol dehydrogenase, 3-β-hydroxysteroid dehydrogenase, glucose-6-phosphate dehydrogenase and sialic acid whereas the levels of testicular acid phosphatase, gamma glutamyl transferase and cholesterol increased dose dependently (P<0.05). The serum luteinising hormone, testosterone and estradiol were reduced after the administration of ethanol extract of S. mombin leaves whereas levels of serum follicle stimulating hormone increased significantly. The 100 and 200 mg/kg body weight of ethanol extract of S. mombin leaves increased the testosterone/estradiol ratios whilst the 500 mg/kg body weight of ethanol extract of S. mombin leaves decreased it. The sperm motility, sperm count, normal sperm morphology, sperm density, sperm viability and semen viscosity were significantly reduced in the ethanol extract of S. mombin leaves-treated guinea pigs (P<0.05) whereas the head-, tail- and neck-defects increased significantly when compared with the control group (P<0.05). In contrast, the semen volume and pH were not significantly altered by the ethanol extract of S. mombin leaves (P>0.05). The ethanol extract of S. mombin leaves at both 100 and 250 mg/kg body weight significantly reduced the total number, circumference, weight and length of the pups whereas the 500 mg/kg body weight of ethanol extract of S. mombin leaves-treated rats did not produce any pup. The 250 and 500 mg/kg body weight of ethanol extract of S. mombin leaves induced degenerative and necrotic changes in the seminiferous tubules with vacuoles in the germinal epithelium and a few to complete absence of spermatozoa. In all of these, the 500 mg/kg body weight of ethanol extract of S. mombin leaves produced the most pronounced alteration on the parameters. Conclusions: S. mombin leaves have induced infertility in the male guinea pigs via endocrine dysregulation, anti-spermatogenic activity, testicular dysfunction and oxidative stress and made possible by the presence of saponins, alkaloids, flavonoids, tannins, steroids, phenolics, and cardiac glycosides.