With　a　batch　type　photocatalytic　reactor,　the　kinetics　of　the　photocatalytic　degradation　of　acetaldehyde　is　investigated　using　gas　chromatography.　It　is　found　that　the　reaction　is　in　photon　transfer　controlled　step　with　high　initial　concentration　of　acetaldehyde　and　low　light　intensity　of　ultraviolet　on　the　surface　of　catalyst,　and　the　reaction　rate　is　proportional　to　light　intensity.　If　the　light　intensity　is　high,　the　degradation　of　acetaldehyde　can　be　described　by　Langmuir-Hinshelwood　equation.　When　the　initial　concentration　of　acetaldehyde　in　the　reactor　is　low,　the　degradation　is　a　typical　first-order　reaction　regardless　of　light　intensity.　With　the　increase　of　the　light　intensity,　the　reaction　rate　constantly　rises.　As　the　light　intensity　exceeds　11.6　W/m2,　the　reaction　becomes　surface　controlled,　and　further　increase　of　light　intensity　has　no　effect　on　the　reaction　rate.