PURPOSE: To obtain hydrogen and oxygen from water and a halogen by a chemical reaction without an electrolysis by reacting water and a halogen and generating hydrogen and oxygen by using an activated carbon as a catalyst.

CONSTITUTION: This production method of oxygen and hydrogen is to use an activated carbon having basic surface functional groups or carrying platinum as a catalyst in a reaction of formula I H2O+X2→2HX+1/2O2 (X is a halogen), react the activated carbon which has absorbed a halogen with water in a reduced atmosphere or irradiate a light to the reaction system, etc. The reaction proceeds to reach an equilibrium state while generating a hydrogen halide and a hypohalogenous acid and to decompose into the hydrogen halide and oxygen by a self decomposition reaction of the hypohalogenous acid as expressed by formula II H2O+X2→HX+HXO and formula III HXO→HX+1/2O2 (X is a halogen). Hydrogen is obtained by a reaction expressed by formula IV 2HX→H2+X2 by heat decomposition at ≤700°C using chromium oxide as a hydrogen halide decomposition promoting catalyst without electrolysis.