This experimental database aimed to obtain the pressure and void fraction wave velocities in air-water slug flow in the vertical orientation. The database contains the raw pressure and dual impedance probe data in a fully instrumented test section. One hundred repetitions for each pair of superficial velocities were performed to filter the intrinsic transient nature of slug flow, especially to obtain the void fraction signal. The test grid encompasses both the increase and decrease in liquid velocity. The system freely achieved the gas velocity. The superficial velocities of liquid varied from 0.30 to 0.60 m/s, and the gas superficial velocities varied from 0.85 to 0.90 m/s at the steady states. The time window for all three experimental points is 6 minutes; this time window is sufficient for the flow to reach a new steady state after the transient. The transient was induced by changing the position of a control valve at 1 minute after the acquisition began.