The mitogen-activated protein kinases (MAPKs) are conserved signal transduction pathways and broadly responsible for bacterial infection from yeast to mammals, and virus, fungi, and bacteria, specifically Bacillus thuringiensis, to insects. But little is known about the MAPK pathways in antibacterial responses in Chilo suppressalis (Walker), an important lepidopteran pest of rice. In this study, we used the bacteria of Bacillus thuringiensis, Escherichia coli, and Staphyloccocus aureus to infect C. suppressalis larvae, and the responses of MAPK pathways were analyzed. The results showed that E. coli infection induced the up-regulated expression of Csp38 and CsERK1 at 24 h postinfection (pi). Meanwhile, injection of B. thuringiensis and S. aureus resulted in strong activation of CsJNK phosphorylation at 3 h pi. These results suggest that MAPK signaling pathways play important functional roles in antibacterial responses in C. suppressalis larvae.