Eukaryotic cells have mechanisms to cope with stress in endoplasmic reticulum (ER) called unfolded protein response (UPR). In this study, we characterized putative X-box DNA binding protein1 (XBP1) and Binding protein (BiP) cDNAs from black tiger shrimp (Peneaus monodon). When the shrimp were infected with Yellow head virus (YHV), the levels of XBP1 and BiP mRNA transcripts were elevated approximately 8 and 55 folds, respectively. In normal shrimp, the putative XBP1 (XBP1u) was predicted to encode a protein with 283 amino acid residues. When shrimp were infected with YHV, portion of cDNA with 17 nucleotides intron elimination (XBP1s) was observed. The elimination caused alteration of its translational frame. The predicted protein from this is 469 amino acids in length with total change in its amino acid sequence downstream of the intron. Functional analysis of these XBP1 proteins in mammalian cells clearly showed that overexpression of P. monodon XBP1s was capable of activating the transcription rate of mammalian UPR responsive genes (BiP, ERdj4 and P58IPK). Finally, the impact of XBP1 and BiP on YHV multiplication in black tiger shrimp was investigated by RNAi approach. Knocking down either XBP1 or BiP expression efficiently inhibited YHV replication. Therefore, these two components in the UPR pathway may be an interesting target for anti YHV development in the future. Keywords: Endoplasmic reticulum, siRNA, Stress-inducible genes, Transcriptional regulation