The formaldehyde oxidation reaction with use of Fenton’s reagent was conducted in a thermostated container with a volume of 1000 ml. An appropriate amount of process iron sulphate (FeSO4×7H2O) was added to 400, 500 and 600 ml wastewater sample containing formaldehyde . The solution was mixed with a magnetic agitator with a velocity of 300 rpm. After FeSO4×7H2O dissolved, an appropriate amount of 30% hydrogen peroxide solution (H2O2) was added. The contents were mixed again for 1, 2 and 3 h. Before and after each hour of conducting the Fenton process, the content of formaldehyde and formic acid was determined in the wastewater.