Flow pattern and the bubble velocity in 2-8 mm diameter inclined tubes were studied in the present work. Experimental observations show that the flow pattern is elongated bubble flow and no small dispersed bubbles exist in the liquid slug in conditions of 0.168-0.672 in s(-1) superficial liquid velocity and 0.04-0.32 m s(-1) superficial gas velocity. The shape of the gas slug in tube is influenced by the diameter of tube, the flow rate, and the inclination angle. Furthermore, the length of gas slug increases with the superficial gas velocity. The length of gas slug in the inclined tube is longer than that in the vertical or horizontal tube, and the gas slug velocity in the inclined tube is faster than that in the vertical or horizontal tube.