A survey on the occurrence of entomopathogenic nematodes (EPNs) was conducted in selected banana fields from three regions in Tanzania, namely Mbeya (Southern Highlands), Morogoro (Lowland) and Pwani (Coast). The main objective of this study was to isolate EPNs naturally occurring in banana fields in Tanzania and to test their effect on banana weevil (Cosmopolites sordidus Germar 1824). We report for the first time the presence of EPNs in Tanzania where four (4.4%) out of 90 samples contained nematodes in the genera Steinernema and Heterorhabditis. EPNs were only isolated in the coastal region in soils with a high sand content. The virulence of nine EPN isolates was tested against larvae and adults of C. sordidus. All isolates caused mortality of the larval stages, whereas the adults appeared resistant to nematode infection. Larval mortality was found to increase significantly with increasing nematode dose. It was also shown that nematodes were able to penetrate and establish in the banana weevil larvae in increasing numbers with increasing nematode dose. The study indicates the potential for including EPNs in management strategies of banana weevil.