Abstract: In this paper, an experimental and theoretical investigation on the characteristics of factional pressure losses of steam - water two - phase flow in helically coiled tubes was conducted in a wide range of system and flow parameters, which are as follows: system pressure p =0.5 -3.5 MPa; mass flow rate G = 200-4300 kg·m-2·s-1; heat flux q =0-580 kW·m-2; exit mass quality x= -0.01- +1.2. The angle between the central axis of helically coiled tube and horizontal line: θ= 0°, + 45°, 90°, - 45°. The experimental results were analyzed and compared with some correlation and data proposed in previous literature. Based on Chens correlation and our experimental data, a new revised correlation was proposed for the calculation of frictional pressure drop of gas liquid two - phase flow in helically coiled tubes oriented with various axial angles. A good agreement was arrived between the calculated values and experimental data.