This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different horizontal tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, floral tube and hydrophilic tube. The additive mass concentration was about 0.05${sim}$5.5%. The heat transfer coefficient was measured as a function of solution flow rate for the range of 0.01${sim}$0.034 kg/ms. The experimental results were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect generated by the addition of the surfactant is observed in each test tube. The increase of heat transfer coefficient by surfactant addition is about 35${sim}$90% for bare tube, 40${sim}$70% for the floral tube, 30${sim}$50% for the hydrophilic tube and was higher for the cases with smaller a little solution flow rates.