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-Bacillus spp. have been used against diseases caused by bacteria that affect cultured shrimp, providing beneficial effects on the host shrimps by altering their microbial community, and improving zootechnical indexes. The objective of this work was to evaluate the effects of a diet supplemented with Bacillus cereus-a bacterium with probiotic potential-on post-larvae Litopenaeus vannamei shrimps grown in laboratory. The experiment lasted for fifteen days and consisted of six treatments-control (T 1 ), probiotic (T 2 ), Vibrio parahaemolyticus (VP) (T 3 ), probiotic and VP (T 4 ), V. alginolyticus (VA) (T 5 ), and probiotic and VA (T 6 ). The survival rate, weight gain, colonization capacity of the probiotic bacteria, pathogen count, and histopathological lesions were evaluated. There was no significant difference (p≥0.05) in survival between treatments. The groups with pathogens and without probiotics presented lower weight gain. The result of the Bacillus cereus count in the treatments T 2 , T 4 and T 6 were significantly different (p<0.05), the probiotic bacteria were more aggressive in competing for space and nutrients when compared to V. parahaemolyticus than when compared to V. alginolyticus. Animals fed with the probiotic presented lower counts of these pathogens than those fed without the probiotic (p<0.05). No histopathological lesions were found in the organs and tissues of the shrimps. Bacillus cereus showed a high colonizing capacity in post-larvae shrimps, causing a significant reduction of pathogens, probably by secreting antimicrobial substances and the competitive exclusion, which justifies their use as probiotic bacteria.Keywords: Litopenaeus vannamei. Antimicrobial. Bacillus cereus. Vibriosis. AVALIAÇÃO DE POTENCIAL PROBIÓTICO FRENTE À INFECÇÃO EXPERIMENTAL POR VÍBRIOS EM PÓS-LARVAS DE CAMARÃO MARINHORESUMO -Bacillus spp. têm sido utilizados contra bacterioses que acometem camarão marinho cultivado, proporcionando efeito benéfico sobre o hospedeiro, alterando a comunidade microbiana intestinal e melhorando índices zootécnicos. O objetivo deste trabalho foi avaliar os efeitos de uma dieta suplementada com Bacillus cereus, bactéria com potencial probiótico em pós-larvas de Litopenaeus vannamei cultivados em laboratório. O experimento teve duração de quinze dias e consistiu de seis tratamentos: T 1 controle; T 2 somente com probiótico; T 3 com Vibrio parahaemolyticus (VP); T 4 com probiótico e com VP; T 5 com V. alginolyticus (VA); e T 6 com probiótico e com VA. Foram avaliados a sobrevivência, o ganho de peso, a capacidade de colonização das bactérias probióticas, contagem de patógenos e lesões histopatológicas. Não foi verificada diferença significativa (P≥0,05) entre os tratamentos na sobrevivência. Os grupos desafiados com patógenos e sem uso de probióticos foram os que apresentaram menor ganho de peso. Na contagem de Bacillus cereus, houve diferença significativa (P<0,05) entre os tratamentos T 2, T 4 e T 6 , observando-se que o probiótico competiu melhor por espaço e nutrientes quand...