The nonstructural protein NSP4, encoded by gene 10 of rotavirus, has been shown to playa role in viral assembly and known to be an enterotoxin, causing diarrhea in mouse pups. NSP4 gene was cloned from CBNU-2 (virulent bovine rotavirus/diarrheic fecal sample) and CBNU-1 (cell-culture adapted bovine rotavirus/isolated from CBNU-2 and 75 times passaged on MA104 cells), respectively, by reverse transcriptase-polymerase chain reaction (RT-PCR) and sequenced and compared. The sequence data indicated that the NSP4 genes of bovine rotavirus (BRV) were 751 bases in length and encoded one open reading frame of 175 amino acids beginning at base 42 and terminating at base 569. Differences in nucleotide sequence between CBNU-2 and CBNU-1 were observed at 6 positions (base 274, 296, 391, 394, 396 and 579). NSP4 gene of BRV exhibited a high degree of nucleotide (90% and 94%) and amino acid sequence (91% and 97%) homology with those of SA11 and UK but a low degree of nucleotide (77% and 79%) and amino acids sequence (81% and 85%) homology with those of Wa and OSU.