Abstract: Experimental study was carried out on the behaviour of single vapor bubbles under subcooling condition in a narrow channel. The effect of subcooling degree was analyzed. Results showed that the single vapor bubbles rose with the decreasing diameter and the changing shape under subcooling conditions. Condensation happened on the interface of single vapor bubbles. Increasing degree of subcooling, the diameter of single vapor bubbles decreased faster. The aspect ratio of single vapor bubbles with the same diameter fluctuated in a scope. Under subcooling conditions, the velocity in z and x direction both first increased then decreased with the increasing diameters. The two velocities both had the maximum value for the bubbles of 10 mm diameter. Larger degree of subcooling induced larger bubble velocity in z direction. The velocity in x direction swung around zero. Increasing the degree of subcooling, the bubble velocity in x direciton increased slightly. The degree of subcooling will affect the behavior of single vapor bubbles in narrow channels, and influence the formation and the evolution of flow regimes in further.