An experimental study was conducted in order to investigate the phase split of annular two-phase flow at a horizontal microimpacting T-junction with the square cross section of 0.5 x 0.5 mm(2). A high speed record camera was used to help elucidate the fluid dynamics at the junction. Nitrogen and water at 120 kPa (abs) and room temperature of 22 degrees C were used as the test fluids. The inlet superficial velocities of gas and liquid varied from 13 to 30 m/s and from 0.018 to 0.08 m/s, respectively, covering a wide range of the inlet qualities between 0.23 and 0.58. The aqueous solutions of sodium dodecysulfate (SDS) and carboxymethyl cellulose (CMC) with different mass concentrations were employed to study the effect of surface tension and viscous force on phase split, respectively. Experimental results showed that, the phase split of annular flow at microimpacting T-junctions was less affected by either the inlet phase superficial velocities or the viscous force, but varied largely with surface tension. Besides, the phase maldistribution of annular flow was smaller than that of slug flow and slug-annular flow at microimpacting T-junctions. Furthermore, when the present data were compared to those of mini- and macro-sized junctions at similar flow conditions, it was found that the phase maldistribution at microimpacting T-junctions was the smallest. Finally, good agreement was obtained between the present experimental data and a modification of an existing model. (C) 2014 Elsevier Ltd. All rights reserved.