Abstract: This piper deals with the establishment of hybridoma cell lines which secrete monoclonal antibcd es ( McABs) against avian infectious bronchitis virus (IBV) Massachusetts strain.BALB/c mice were immunized with the antigens of IBV which was grown in embryonated eggs and parified using differential and sucrose gradient centrifugation.Spleen cells from the immunized mouse were fused with SP2/0 mouse myeloma cells.Screened by both indirect ELISA and PHA,and subcloned two or three times,three hybridoma cell lines namely E11,2D6,4B10 secreting spscific McAbs to IBV were established.Results showed that the chromosome numbers of hybridoma E11,2D6 and 4 B10 were 98,97,and 94 respectively.Those McAbs were found to belong to subclass 1 of murine IgG and showed the single band in the gamma globulin region of PAGE electrophoregram.The supernatant of hybridoma cell cultures had a titer of 1 to 1/4 measured by PHA and 1/100 to 1/800 by ELISA,and the ascites fluid had a titer of 1/16 to 1/64 measured by PHA and 1/50000 to 1/500000 by ELISA.The specificity of McAbt to IBV was proved by the results of competitive ELISA.The hybridomas were still stable in their ability to secrete McAb after they were preserved in liquid nitrogen for four months.A further study on other characteristics of those McAbs and attempt to apply them to use are being undertaken.