Abstract: A series of co-current gas-liquid flow pattern experiments with two inclination angles were conducted in a 15mm diameter, 6m long acrylic pipe installed on an inclinable trestle. Flow patterns determination and classification were based on the visual observations and the characteristics of pressure differen tial fluctuation, and according to the experimental data, flow pattern maps with different inclination angle were drawn. In addition, through the comparison with the flow pattern map in the same diameter horizontal pipe and the range of flow pattern with different inclination angle, it was found that the inclination angle had a prominent effect on the flow pattern region.