This study screened the antidiarrhoeal, antimicrobial and cytotoxic effects of ethanol-extracted leaves of yellow oleander (Thevetia peruviana). The extract was tested against castor oil-induced diarrhoea in a model of albino rats and showed significant antidiarrhoeal activity (P<0.01). Disc diffusion technique was used to test the in vitro antibacterial activities of the extract and exhibited poor antibacterial activities against both Gram positive and Gram negative bacteria (mainly Bacillus sp). Ethanol-extracted leaves of yellow oleander showed narrow zone of inhibition in the bacterial lawns of Shigella flexineri, Salmonella typhi, Klebsiella sp, Staphylococcus aureus and Shigella sonnei. Cytotoxicty was determined against brine shrimp nauplii and LC50 of the plant extract was determined as 627.21μg/ml. The wide range of LC50 value denotes the safety effect of the extract.