A model is developed to calculate the transient behavior of co-current gas-liquid flow with small liquid holdup values (epsilon (L) less than or equal to 0.1) through a horizontal regular T-junction. The present model combines transient two-phase pipe flow and gas-liquid Row splitting in a T-junction. The transient model has been derived from the mass and momentum balances for the gas and liquid phase. The splitting model has been derived from the steady-state macroscopic mechanical energy balance (extended Bernoulli equation) applied to the "inlet-to-run" streamline acid "inlet-to-branch'' streamline of both the gas and the liquid phase. The calculated results with the introduced transient model are compared with experimental data of the transient how of the system air;water through a horizontal regular (D-1 = D-2 = D-3 = 0.051 m) T-junction. The calculated steady-state values as well as the time-dependent dynamic changes of gas-liquid flow through a horizontal regular T-junction are in good agreement with the on-line registered experimental data.