Abstract: Acyrthosiphon pisum is a major crop pest found worldwide. It causes significant damage to legumes. The A. pisum is a model organism for biological studies. The aim of the work is to develop effective control methods for this pest species. A computational approach to identify genes for stress response, immune response, recognition and signaling was performed. The four unassembled ESTs libraries namely antennae, head, digestive tract and whole body were taken for the study. The functional annotation was done for four EST libraries by Blast2GO software. Local BLAST was performed with the assembled transcriptome sequence (GenBank: SRX316762) for gene expression analysis. The complete ORF of screened were predicted in ORF finder and validated by SmartBlast tool. Further, the proteins were characterized using several tools and servers: signal peptide by SignalP 4.0, physiochemical properties by the ProtParam tool, sub-cellular localization by ProtComp V9. The analysis revealed 26 genes expressed during microbial infection. Genes were further categorized into four ontologies: stress response, immune response, recognition and signaling. The signal peptide was present in 9 proteins. The aliphatic index, excitation index, instability index, theoretical points, molecular weight, amino acids residues, positively and negatively charged residues and grand average of hydrophobicity were the physiochemical properties studied in the proteins. From subcellular localization cytoplasmic, nuclear, mitochondrial, endoplasmic reticulum, plasma membrane and extracellular proteins were obtained.