Abstract: The explosive characters of ClO2 gas were investigated in a cylindrical explosion chamber of 20 liters capacity. Experimental results indicate that the lowest volume fraction of ClO2 gas for its explosive decomposition is 9.5%, and the corresponding highest volume fraction is no existent. Under these experimental conditions, the explosion pressure of ClO2 gas increases with its increasing volume fraction, its maximum explosion overpressure is 0.64 MPa when its volume fraction is 90%, and its explosive decomposition pressure is relevant with its volume fraction gradient. The appearance time of the maximum explosion overpressure is advanced with the increasing volume fraction of ClO2. When the volume fraction of ClO2 is 10%, the maximum explosion overpressure appears at 2 195.00 ms.When the volume fraction of ClO2 is 70%, the maximum explosion overpressure appears at less than 10 ms. If the volume fraction of ClO2 continues to increase, the appearance time of the maximum explosion overpressure keeps at about 8 ms.