Polymeric immurnoglobulin receptor (pIgR) is an important fish mucosal immune factor, which plays a key role in mediating the secretion and transport of polyimmunoglobulin into the mucus of mucosal immune tissue. In this study, the full-length cDNA sequence of Aristichthys nobilis pIgR gene was cloned using PCR and RACE technology. The full-length cDNA sequence of Aristichthys nobilis pIgR gene was 1885 bp, and its open reading frame (ORF) was 1008 bp, encoding 336 amino acids. Aristichthys nobilis pIgR had a signal peptide sequence, followed by the extracellular region, transmembrane region, and intracellular region. The extracellular region included two immunoglobulin-like domains (ILD), and its tertiary structure was twisted “L”. The phylogenetic tree was constructed using the NJ method. The results showed that the pIgR gene of Aristichthys nobilis was clustered with the pIgR of cypriniformes. The expression level of the pIgR gene in different tissues of Aristichthys nobilis was detected using quantitative real-time PCR (qRT-PCR). The highest expression level of pIgR gene was found in the liver, followed by the spleen, intestine, head kidney, gill, and skin. A low expression level was found in the middle kidney, heart, and brain, and the lowest expression level was found in the muscle. Aristichthys nobilis was infected with Aeromonas hydrophila at 5 d. The pathological changes in immune-related tissues with a high expression level of the pIgR gene were observed using tissue sections and HE staining. It was found that the intestinal villus mucous cells increased, the width of the intestinal villi widened, and the intestinal wall thickened, showing prominent symptoms of intestinal inflammation. Many inflammatory cells appeared in the head kidney and spleen, and many vacuolar cells were observed in the spleen. The width of the hepatic sinuses increased. The gill filament was deformed and shortened, and the gill cell withered. The expression level of Aristichthys nobilis pIgR gene in the gill, intestine, spleen, liver, and head kidney increased first and then decreased within 28 d after being infected with Aeromonas hydrophila. The relative expression of pIgR gene reached the peak at 5 d in the intestine and gill, and reached the maximum at 7 d in the head kidney and 14 d in the spleen and liver after infection, respectively. The relative expression level of the pIgR gene at the peak in the intestine (18.63 fold) and gill (16.53 fold) of Aristichthys nobilis was higher than that in the head kidney (9.38 fold), spleen (15.98 fold), and liver (12.28 fold). The experimental results showed that Aeromonas hydrophila infection not only caused immune-related tissue lesions and triggered the inflammation responses but also affected the respiratory system and digestive system of Aristichthys nobilis. pIgR may play a key role in the mucosal immune system of Aristichthys nobilis against bacterial infection.