BACKGROUND: Standardized leaf extract of Gingko biloba (EGb 761® ) is a modern herbal medicinal product. It is one of the bestselling and popular botanical drug preparations in the world. OBJECTIVES: The study was carried out to evaluate the phytochemical constituents of Ginkgo biloba leaf extract (EGb 761® ), to determine the effect of the extract on erythrocyte osmotic fragility under hypotonic stress, and to investigate the effect of the extract on haematological parameters and erythrocyte osmotic fragility in rats experimentally exposed to chlorpyrifos-induced oxidative stress. METHODS: A total of 35 adult albino rats, divided into 7 groups of 5 rats each, were used. Group A served as control, Groups B and C were pre-treated and post-treated with vitamin E respectively, while Groups D and E were pre-treated and post-treated with EGb 761® respectively before administration of chlorpyrifos. Groups F and G were only treated with the extract and chlorpyrifos respectively. RESULTS: The findings showed that there was no significant difference in erythrocyte osmotic fragility between pre-treatment and post-treatment with EGb 761 in chlorpyrifos induced oxidative stress (P>0. 05). However, the erythrocytes of rats treated with EGb 761® were significantly more resistant to hypotonic haemolysis in comparison to vitamin E and control (P˂ 0. 05). Pre-treatment with EGb 761 resulted in significantly higher packed cell volume, haemoglobin concentration, and red blood cell counts than pre-treatment with vitamin E and control (P˂ 0. 05). Also, post-treatment with EGb761® significantly increased total protein in comparison to control (P˂ 0. 05). CONCLUSIONS: It was concluded that EGb 761® administration resulted in increased erythrocyte resistance to haemolysis and increased blood cellular components.