This　paper　presents　investigations　on　the　effect　of　a　surface　active　agent　on　the　characteristics　of　air/water　two-phase　flow　in　horizontal　and　inclined　pipe　using　the　electrical　conductive　tomographic　technique.　Air/water　and　air/100　mg/kg　sodium　dodecyl　sulphate　(with　95%　purity　grade)　aqueous　solution　are　used　as　working　fluids.　For　2.5°　and　5°　pipe　inclinations,　the　surfactant　has　obvious　effect　on　the　transition　from　stratified　wavy　flow　to　annular　flow.　For　10°　pipe　inclination,　no　stratified　flow　regime　is　observed　in　the　air-water　flow.　In　the　air-surfactant　solution　system,　however,　stratified　flow　regime　has　been　found　to　exist　in　the　range　of　USG　=　10　-　28　m/s　and　USL　=　0.07　-　0.2　m/s.　No　obvious　change　is　observed　for　the　transition　between　plug　flow　regime　and　slug　flow　regime.