The　influence　of　a　surfactant　on　the　two-phase　flow　regime　and　the　pressure　drop　in　upward　inclined　pipes　is　investigated　for　various　gas/liquid　flow　rates.　The　air/water　and　air/100　ppm　sodium　dodecyl　sulphate　aqueous　solution　are　used　as　the　working　fluids.　The　influence　of　the　surfactant　on　the　two-phase　flow　regime　in　upward　inclined　pipes　is　investigated　using　the　electrical　tomographic　technique.　For　0　degrees,　2.5　degrees　and　5　degrees　pipe　inclinations,　the　surfactant　has　obvious　effect　on　the　transition　from　the　stratified　wavy　flow　to　the　annular　flow,　and　the　range　of　the　stratified　smooth　flow　regime　is　also　extended　to　higher　gas　velocities.　For　100　pipe　inclination,　no　stratified　flow　regime　is　observed　in　the　air/water　flow.　In　the　air/surfactant　solution　system,　however,　the　stratified　flow　regime　can　be　found　in　the　range　of　U-SG　=10　m/s-28　m/s　and　U-SL　=　0.07　m/s-0.2　m/s.　For　all　inclination　angles,　the　changes　of　the　pressure　gradient　characteristics　are　accompanied　with　the　flow　pattern　transitions.　Adding　surfactant　in　a　two-phase　flow　would　reduce　the　pressure　gradient　significantly　in　the　slug　flow　and　annular　flow　regimes.　In　the　annular　flow　regime,　the　pressure　gradient　gradually　becomes　free　of　the　influence　of　the　upward　inclined　angle,　and　is　only　dependent　on　the　property　of　the　two-phase　flow.