We synthesize the powder of the precursor of TiO2, which shows the giant electrorheological effect but does not include the component of CaC2O4H2O. By use of X-ray diffraction, scanning electron microscope, inductively-coupled plasma spectrometer, themogravimetry-mass spectrum, etc, it is found that the precursor of TiO2 is amorphous powder with nanosize, and its components include TiOC2O42H2O and TiO(OH)2. The electrorheological fluid made by the powder shows a similar temperature characteristic to that made by the precursor of CaTiO3, i.e., when the powder is heated to the temperature above 160℃, the yield stress of the electrorheological fluid made by it decreases gradually, and when it is heated to 200℃, the giant electrorheological effect disappears completely. It is also found that the chemical reaction accompanies with the disappearance of the giant electrorheological effect is that the crystalized water in TiOC2O42H2O is volatilized in heating process. These characteristics can be observed in all electrorheological fluids made by the precursor of other titanate, so we conclude that TiOC2O42H2O is the key component for this series of giant electrorheological fluids.