There are thermolable and thermostabile antigen in colibacilli antigen, but the correspondence for heat of antibodies which was obtained from immune rabbit with them was quite contrary when compared with the corre-spondence for heat of antigens. Antibody which was immunized with thermostable antigen lost half its agglutinin and precipitin by heating for 20 minutes at 65°C and these substances were almost destroyed at 75°C and completely at 90°C. While, antibody which was immunized with thermolabile antigen lost a little their strength by heating for 20 minutes at 65°C and these substances were almost destroyed at 75°C, but were noticed being remained a little even at 90°C. Agglutination and precipitation (Ogata Method) of O and H antibody were noticed being diminished in parallel with heat. Therefore, agglutinin and precipitin are considered to be both unitary.