Two　kinds　of　nanoscale　TiO　2　films　were　prepared　by　magnetron　sputtering　and　screen　printing　methods,　respectively.　Results　show　that　both　phase　composition　and　specific　surface　area　of　the　film　affect　the　photocatalytic　bactericidal　efficiency.　Time-series　in　situ　atomic　force　microscopy　(AFM)　observation　were　further　used　to　characterize　the　cellular　responses　of　Escherichia　coli　(E.coli)　in　photocatalytic　process.　Some　nanosized　patches　were　found　on　the　bacterial　surface　in　the　forepart　of　photocatalytic　reaction.　It　suggested　that　the　photocatalytic　attack　induced　the　selfprotection　of　bacteria　at　first.　Subsequently,　some　cracks　on　the　surface　and　the　enlargement　of　cell　body　indicated　that　the　cell　wall　was　damaged　and　lost　its　structure　supporting　function,　and　it　eventually　led　to　the　death　of　bacteria.　Copyright　©　2011　American　Scientific　Publishers.　All　rights　reserved.