Plutella xylostella , is the main pest infesting Brassica crops, and products based on Bacillus thuringiensis (Bt) are frequently used in strategies for its biocontrol. The present study aimed to evaluate whether a Bt-based bioinsecticide affects the predation behavior of Ceraeochrysa cincta when preying on P. xylostella . Three larval instars of the predator and the eggs and second-instar larvae of the moth were used, with the prey either untreated or treated with a Bt-based product (Xentari®). Results showed that, the first larval instar of C. cincta presented a type II functional response when preying upon untreated eggs, and a type III response when preying upon Bt-treated eggs, while the second and third instars presented type II and III responses, respectively, in both situations. The predator’s first and third larval instars presented a type II functional response when preying upon untreated larvae and a type III response when preying upon Bt-treated larvae. However, the predator’s second-instar larvae showed a type II response in both treatments. The results obtained allowed us to conclude that the Bt-based insecticide tested affects the predation behavior of the first-instar larvae of C. cincta on eggs and of both the first- and third-instar larvae of this predator on P. xylostella larvae.