The NF-kB signaling pathways including Imd and Toll pathways play a major role in insect host defense through recognition of microbial infections and triggering appropriate immune responses. During infection, the Toll and Imd pathways control the expression of hundreds of genes including antimicrobial peptides and many other peptides and proteins. In this study, we identified and experimentally confirmed expression of the important genes involved in Imd and Toll pathways of the cotton bollworm, Helicoverpa armigera. To identify these genes in H. armigera genome, we considered mRNAs from whole transcriptome sequences and ESTs extracted from NCBI as well. By BLAST search we found Imd and Relish (involved in Imd pathway), and Spatzel and Dif (involved in Toll pathway), in the transcriptome dataset of this insect. To find whether these genes are expressed in different developmental stages of H. armigera (i.e. the eggs, first to sixth instars larvae, pre pupa, pupa and adults), total RNA was extracted from each stage and cDNA library was synthesized by using RT-PCR and oligodt primer. Transcript levels of the genes were analyzed by RT-qPCR utilizing 18s rRNA and Actin as the reference genes. To see if these genes have any role in bacterial infection, we challenged the fifth instar larvae of the cotton bollworm by injecting Serratia marcescens or Escherichia coli cells into the hemolymph while the control larvae were injected with ds water instead. Total RNA was extracted from the treated and the control larvae at different times post injection and the transcript levels of the target genes were analyzed. The results showed that all the assessed genes were expressed during development of H. armigera. Expression level of Imd was higher than that of the other genes. We found that the expression levels of Imd, Relish, Dif, Spatzle genes were diminished in the S. marcescens -injected larvae while there it increased in response to E. coli injection. There was no change in the expression levels of the control larvae. These results show that S. marcescens is able to suppress Imd and Toll pathways thereby inhibit humeral immune response of H. armigera. The mechanisms that S. marcescens undertaking to suppress these pathways remains to be investigated.