TiO2　catalysts　were　prepared　from　a　TiO2　sol　by　microwave　heating　and　conventional　heating,　respectively.　A　microwave-light　reactor　equipped　with　a　high　frequency　microwave　source　and　UV　light　source　was　used　to　investigate　the　effect　of　microwave　on　the　photocatalytic　degradation　and　product　distribution　of　acetaldehyde　over　both　samples　obtained　above.　The　results　showed　that　the　sample　prepared　by　the　microwave　heating　presented　higher　photocatalytic　activity　and　stronger　oxidative　ability　to　acetaldehyde　than　that　obtained　by　conventional　heating.　There　were　different　oxidative　pathways　on　the　two　catalysts:　the　initially　reactive　intermediates　were　formaldehyde　and　formic　acid　on　the　sample　by　microwave　heating,　and　acetic　acid　on　the　sample　by　conventional　heating.　It　was　also　found　that　microwave　had　different　effect　on　the　photocatalytic　conversion　of　acetaldehyde　for　two　samples.　The　effect　was　more　remarkable　for　the　sample　prepared　by　the　microwave　heating　than　that　prepared　by　the　conventional　heating.　Enhanced　photocatalytic　capacity　of　TiO2　by　microwave　mainly　was　from　a　field　effect,　which　can　accelerate　a　transform　of　the　initial　intermediates　but　does　not　change　the　photocatalytic　pathway　(the　pathway　depends　on　the　properties　of　catalyst).