The feline coronaviruses (FCoVs), belonging to the family Coronaviridae, order Nidovirales, are responsible of an inapparent or mild enteric infection, but also cause a progressive, fatal immune-mediated disease, feline infectious peritonitis (FIP), predominantly in the cats from multiple-cat households. The FCoVs virion contains three principal structural proteins: the S spike protein, the M membrane protein and the most representative nucleocapsid protein N. The N protein binds viral RNA to form a helical core structure during virion assembling and together with the M protein is a component of the viral core; in addition to its structural role, the N protein also participates in viral RNA transcription, replication, translation and in modulating the metabolism of host cells. Several studies have identified antigenic determinants in the N protein of human and animal coronaviruses and have demonstrated that the N protein is one of the immunodominant antigens in the CoV family. The aim of this study was to investigate the antigenic role of the N protein, carrying out detailed phylogenetic and computational analysis of the N protein sequences of FCoV strains detected in healthy and diseased cats. Preliminary results confirm a possible involvement of the nucleocaspid protein in the cell immune-mediated response.