Classical mumps patients develop bilateral or less commonly unilateral parotitis. Mumps virus belongs to the genus Rubulavirus in the family Paramyxoviridae. It contains single stranded RNA genome with negative polarity. To characterize the antigenicity of mumps virus isolated in Korea, nineteen hybridoma cell lines producing monoclonal antibodies to mumps virus were established by fusion of Sp2/0-Ag14 mouse myeloma cells with spleen cells of mice immunized with mumps virus strain 98-40. The specificity of these monoclonal antibodies was established by immunofluorescence microscopy and immunoblotting analysis. Fifteen out of nineteen hybridoma cell lines secreted IgG monoclonal antibodies (MAbs) against mumps virus, and the remaining four secreted IgM. The isotypes of thirteen clones of 19 MAbs were IgG1, two were IgG2a, and four were IgM. Eight MAbs reacted with a 68 kDa nucleocapsid protein, six MAbs reacted with a 46 kDa phosphoprotein, and five MAbs reacted with a 42 kDa matrix protein.