Abstract: Carica papaya methanol leaf extract (CPMLE) is used widely in West Africa as anti-malarial and antimicrobial. The aim of this experiment was to study the effects of (CPMLE) on fertility in male Wistar rats using sperm counts and percentage of defective sperm cells as markers. Acute toxicity test was performed. Thirty-two male Wistar rats were divided into 4 groups and treated orally with 100, 200 and 400 mg kg-1 b.wt., respectively with the extract. Group 4 served as control (10 mL kg-1 distilled water). After 28 days of treatment, serum biochemical parameters including Aspartate aminotransferase (AST), Blood Urea Nitrogen (BUN), Total Bilirubin (TB), alkaline phosphatase (ALP), alanine aminotransferase (ALT), gamma glutamyltransferase (GGT), triglycerides, total protein and albumin and histopathological study of the testes, kidney, heart and liver were assayed. Acute toxicity results showed that CPMLE produced no mortalities at the dose of 1500 mg kg-1. However, there were CNS signs as well as diuresis. CPMLE significantly (p<0.01) produced dose dependent decreases in sperm counts and increased the percentage of defective sperm cells. There were significant (p<0.05) increases in AST and BUN. Histopathological studies showed mild kidney and cardiac hyperaemia, slight hepatic degeneration and severe necrosis of the germinal epithelium of the testes. These show that CPMLE can produce some defects to fertility and may be used to control birth rate.