A disturbance wave in boiling flow was experimentally investigated through film thickness measurements in a steam-water system as well as flow visualization in a Freon-113 system. Comparing the results with the corresponding adiabatic flow data, we established a new kind of hydrodynamic non-equilibrium, and identified it with that in liquid distribution between the base film and the bodies of the disturbance wave. The decaying process of this non-equilibrium was examined in detail in a non-heated section. Interaction of the disturbance wave with the dryout phenomenon was then clearly demonstrated. Finally, the effects of artificial hydrodynamic non-equilibrium associated with the disturbance wave were discussed.