Abstract: The properties of oscillatary states caused by Bang-Bang control of non-isothermal and non-adiabatic fixed bed reactor have been studied experimentally. In o-xylene catalytic oxidation the phthalic anhydride yield with Bang-Bang control may be higher than that in the steady state operation by about 3% (mol/mol). The causes of higher yield of phthalic anhydride with dynamic operation were also discussed. Compared with the classical setting value control method, Bang-Bang control may provide another measure tor engineering control and provide greater operating flexibility.