Four strains of laIVicidal bacilli isolated from soil and dead mosquito lalvae inrnEthiopia and two intemational standard strains, Bacillus tituringiensis var.rnisraelensis; IPS-82 and Bacillus sphaericus, SPH-88, were investigated for theirrnlalvicidal potential using laIVae of the mosquito species, Culex: quinquefasciatusrnand Anopheles arabiensis. Among the four media types selected for cultivation ofrnthe strains, medium-2 and medium-3 were found suitable to enhance the toxicityrnof the Ethiopian strains. Moreover, culture incubation temperature and aerationrnrate were found to affect the laIVicidal potential of the Ethiopian strains. ThernlaIVicidal efficacy (LCso values) of the Ethiopian strains ranged from 0.0086 mgllrnfor Bacillus NA-82 on second instar laIVae of Cx. quinquefasciallls to 221.6 mgllrnfor Bacillus NA-6 on third instar laIVae of All. arabiensis. IPS-82 showed thernhighest laIVicidal efficacy with LCso value of 0.0010 mgll against secondrninstar laIVae of All. arabiensis. Two of the Ethiopian strains and IPS-82 showed arnhigher toxicity on larvae of All. arabiensis than on Cx. quinquefasciallls. AllrnEthiopian strains have high degree of morphological and biochemical similaritiesrnto the reference strain of B. tilllringiensis var. israelensis (IPS-82) and have beenrntaxonomically classified as strains of B. Ihuringiensis. Moreover, serologicalrncharacterization revealed that two of the Ethiopian strains, Bacillus NA-6 andrnBacillus NA-71 are identical to B. tJllIringiensis var. seoulensis. The other twornstrains, Bacillus NA-IO and Bacillus NA-82 showed low level of titers to two ofrnthe type antisera tested and thus are possibly new serotypes of B. IJllIringiensis.