Bubble pump is an equipment that pumps liquid by using the buoyancy of bubbles. Generally, it is used when conventional pumps are not suitable. The simplicity in structure is the advantage of the bubble pump. In addition, it can pump with high-temperature liquid or liquid with sediments. The objective of this study is to examine the efficiency change by varying the contact angle of the riser surface. Three different squared bubble pump riser surfaces were used in this experiment, each having both width and length of 11mm, 8mm, 5mm with the submergence ratios in the range of 0.3~0.7. Also, five contact angles of riser surfaces in the range of 23.7o~153.8o were prepared in order to vary the wettability of the riser surface. The efficiencies of bubble pump were studied in relation to the sizes of the riser, submergence ratios and contact angles of water with the riser surface of the bubble pump. The experiments were conducted by varying the flow rate of the bubble. A correlation equation of flow rate discharged liquid from the bubble pump was obtained. It was compared the riser surfaces with the maximum efficiency and also the riser surfaces that were uncoated. With a decrease in the diameter and increase of the submergence ratio, the maximum efficiency is found at lower gas flow rates. Also, the efficiencies for 11mm, 8mm, 5mm riser surfaces with the contact angle of 90.3o enhanced by 22.5%, 25%, 18% respectively, comparing to uncoated riser surface where the contact angle 60.8o. In the case of superhydrophobic surface, where the contact angle is 153.8o, the reversed liquid vibration flow was generated, lowering the efficiency of the bubble pump. In conclusion, a correlation equation of volumetric liquid flow rate with respect to the riser surfaces of bubble pump, flow rate of bubble, submergence ratio and aspect ratio was obtained, within ±20% deviation.