Abstract: Experimental investigation was carried out to study the characteristics of void wave for up-wards gas-liquid flow under external disturbances using double-ring conductance probes. The results show that the void wave exhibits the frequency selectivity to the periodical disturbances exerted. In the bubbly flow regime, low frequency external disturbances can induce void wave, whose frequency is almost equal to that of external disturbances. In the bubble-to-slug transition regime, low frequency external disturbances accelerate bubble coalescence and lead to bubble-to-slug transition. In the slug regime, however, external disturbances have little effect on the characteristics of void wave. Void wave velocity decreases first and then increases with the increasing of disturbance frequency. A critical disturbance frequency was found in the present experimental investigation. The effect of external disturbances on the void wave is most significant under the critical disturbance frequency. The critical frequency obtained in current experimental study was about 20 Hz.