Experimental data al e presented for the gas velocity, the void fraction, and the pressure drop of upward co-current air-water two-phase flow through vertical miniature triangular channels having hydraulic diameters of 0.866, 1.443 and 2.886 mm, with superficial air velocity ranging from j(g) = 0.1 to 100 m/s and superficial water velocity ranging from j(l) = 0.08 to 6 m/s. A correlation is developed for predicting the pressure drops of single-phase laminar and turbulent flow through the miniature triangular channels based on that proposed by Churchill (S.W. Churchill, Friction-factor equation spans all fluid flow regimes, Chem. Eng. 84(24) (1977) 91-92) for circular tubes. This work shows that the pressure drop of two-phase Row in the miniature triangular channels call be well predicted by the Lockhart-Martinelli correlation (R.W. Lockhart, R.C. Martinelli, Proposed correlation of data fur isothermal two-phase two-component flow in pipes, Chem. Eng. Frog. 45 (1949) 39-48) if the newly proposed friction factor correlation for single-phase Row is adopted.