Vi is a linear homopolymer of 1,4 N-acetyl galactosaminuronic acid. It is present in S. typhi and some other members of Enterobacteriaceae. Vi antigen of S. typhi has been associated with the virulence of the organism and a vaccine based upon this antigen has been found to confer immunity against typhoid. In this paper, we report production and characterization of four hybrid cell clones secreting monoclonal antibodies against Vi capsular polysaccharide. Binding analysis using different derivatives of Vi showed that three monoclonal antibodies reacted with the antigenic determinant constituted by O-acetyl group and one recognised the epitope constituted by N-acetyl and carboxyl groups together. All the antibodies bound to Vi positive strains of S. typhi and did not show any significant reactivity with Vi negative strains of S. typhi, S. paratyphi A, S. paratyphi B and E. coli. Besides their utility in studying the sub-specificity of antibodies produced after vaccination with Vi, these antibodies would be helpful in the diagnosis of typhoid fever.