Prediction of flow conditions at which slugs are formed and characterisation of slugging are critical technological problems that are not fully resolved yet. This study experimentally and numerically investigated the characteristics of air/water slug flow by documenting the effect of different air and water superficial velocities on water slug length and frequency. The investigations focused on slug frequency, slug length, slug initiation in the pipe and liquid holdup. Experiments were conducted using a 0.074-m-diameter horizontal acrylic pipe with an 8.0-m length. A high-speed video camera was used to obtain the image sequence of the slug flow covering ranges of 0.7-3.5 and 0.65-1.23 m/s air and water superficial velocities, respectively. Numerical simulations were performed using a 3D implicit unsteady volume of fluid model with STAR-CCM+ code. The comparison of simulation experiments exhibited a reasonable agreement within a 10.4 relative error. The time traces of water holdup indicated that slugs are formed as a result of local instability at the wave crest rather than due to the instability of the entire wave. Mean water slug lengths ranged within 3.5-15 Dpipe. By increasing the air superficial velocity by 50 and fixing the water superficial velocity, the slug frequency decreased by 0.25 Hz. When the air superficial velocity was fixed and the water superficial velocity increased by 50, the frequency rate was increased by 1.88 Hz. © 2020 Penerbit Akademia Baru.