Histomorphological assessment of the testes of mice exposed to the ethanolic seed extract of Mucuna urens were investigated in 24 male mice weighing between 20 – 30g. The mice were divided into four groups of six mice each. Group 1 was the control, while group 2, 3 and 4 were the experimental groups. 80 seeds of Mucuna urens were macerated and the content was extracted using 1000mls of absolute alcohol, filtered and dried in water-bath at 45°C. 1000mg of the extract was dissolved in 50mls of distilled water and 50mls of 30% tween 80. The extract was administered orally for 7 days. Group 1 was administered 5ml distilled water, group 2 were administered 100mg/kg of ethanolic seed extract of Mucuna urens, group 3 were administered 200mg/kg of ethanolic seed extract of Mucuna urens and group 4 were administered 300mg/kg of ethanolic seed extract of Mucuna urens. After sacrifice, the testes was harvested and fixed in 10% buffered formalin, dehydrated in alcohol, cleared in xylene, infiltrated in molten paraffin wax and embedded. The tissues were processed to paraffin sections, cut at 5 microns, stained in H&E staining technique and the cytoarchitecture was viewed with light microscope. Photomicrograph of group 1 showed normal blood vessels, seminiferous tubules and interstitial connective tissues. Photomicrograph of group 2 showed lesion blood vessels, shrinking seminiferous tubule and mild eroded interstitial connective tissues. Photomicrograph of group 3 showed hemorrhage, severely shrinking seminiferous tubules and severely eroded interstitial connectively tissue. Photomicrograph of group 4 showed degenerated blood vessels, degenerated seminiferous tubules and severely eroded interstitial connective tissues. Severity was dependent on dose and duration. The ethanolic seed extract of Mucuna urens may lead to fertility impairment by altering the ultrastructure of the testes.