Immunoreactive polypeptide profiles study was made in the whole cyst lysate antigen of Sarcocystis fusiformis which was collected from buffaloes slaughtered at local slaughterhouse, Mathura, U.P. When whole cyst lysate antigen was subjected to SDS-PAGE, twelve major polypeptides (78, 66, 53, 50, 42, 39, 32, 29, 27, 24, 19 and 15kDa) were observed. On western blotting, out of twelve, six (32, 39, 42, 53, 66, 78kDa) and two polypeptides (53kDa and 66kDa) were found to be immunoreactive when probed with homologous hyperimmune and pooled known positive natural serum. No immunoreactivity was seen with pooled known negative natural serum. These two polypeptides (53kDa and 66kDa) bands can be explored for the development of sensitive and specific diagnostic assays.