Provided is a method of separating carbon and oxygen isotopes by using a laser. In one preferred embodiment, the method includes performing a photolysis process on formaldehyde including a carbon or oxygen isotope by irradiation with ultraviolet light having a wavelength ranging from 340 nm to 360 nm to generate carbon monoxide having a carbon or oxygen isotope enriched therein and hydrogen, performing a catalytic reaction on the carbon monoxide having a carbon or oxygen isotope enriched therein and the hydrogen to synthesize carbon dioxide (CO2) and water (H2O) having a carbon or oxygen isotope enriched therein, and cooling the H2O to recover CO2 having a carbon isotope enriched therein or H2O having an oxygen isotope enriched therein.