Mangifera indica Linn, a plant widely used in the traditional medicinal systems of India, has been reported to possess antiviral, antibacterial and anti-inflammatory activities. In the present study, the alcoholic extract of stem bark of Mangifera indica Linn (Extract I containing mangiferin 2.6%), has been investigated for its effect on cell mediated and humoral components of the immune system in mice. Administration of test extract I produced increase in humoral antibody (HA) titre and delayed type hypersensitivity (DTH) in mice. It is concluded that test extract I is a promising drug with immunostimulant properties.