Using reverse transcription-nested Polymerase Chain Reaction(RT-nested PCR), the S1 gene hypervariable regions of Avian Infectious Bronchitis Viruses(IBV) strains BJ1, BJ2, BJ3, isolated from Beijing areas, were amplified successfully. The region consists of 1054 bp of 5'-end of S1 gene which were regarded as the most variable region among IBV strains. Sequences of the S1 gene were determined from recombinant plasmids by using the dideoxy sequencing technique in two directions. Comparing three isolates with standard strains M41, Beaudette, vaccine strain H120 and one isolated strain D41 from Guangdong province, it was shown they were more homology in nucleotide sequence and deduced amino acid sequence with M41 than Beaudette and H120. However, secondary structure of their encoding proteins are more similar with H120 than M41 and Beaudette strains. All of these indicate there are complex relationship among difference of nucleotide sequence, changes of virus determinants and serotypes in Infectious Bronchitis Virus.