The flagella antigenic variation of nine Bacillus thuringiensis serovar kurstaki temperature-sensitive mutants grown at the permissive temperature (3$0^{circ}C$) was detected by a serological agglutination between H-antigen and antiserum. The flagella antigens were injected to rabbits to prepared their antisera, and then their homologous and heterologous titers of the antisera were measured. The homologous titers were ranged from 1:6,400 to 1:12,800, but the heterologous titers were very low. The H-antigen of the wild type strain was not agglutinated to 4 heterologous antisera, ts-U23 not to 7, ts-U3l not 5, ts-U32 not to 4, ts-U33 not to 7, ts-U7l not to 4, ts-U73 not to 6, ts-U74 not to 6, ts-U91 not to 4 and ts-U603 not to 4 antisera.