This is part two of a two-part study that investigates water pressure drop across a staggered array of circular micro-pin-fins. This paper reports results of adiabatic liquid-vapor two-phase flow, and part one isothermal liquid single-phase flow. The micro-pin-fins are 180 mu m in diameter, 683 mu m in height, and 399 mu m in both longitudinal and transverse pitches. Seven maximum mass velocities from 171 to 491 kg/m(2) s, and sixteen vapor qualities for each maximum mass velocity were tested. Two-phase pressure drop across the micro-pin-fin array was measured, and two-phase friction multiplier and Martinelli parameter calculated. It was revealed that a unique functional relationship exists between the two-phase friction multiplier and Martinelli parameter, which proved that the generalized procedure developed by Lockhart and Martinelli could be applied to describe two-phase pressure drop across the micro-pin-fin array. The existing Martinelli-Chisholm type correlations for staggered micro-pin-fin arrays and tube banks were unable to predict the data, and a new correlation was developed. (C) 2015 Elsevier Ltd. All rights reserved.