In two-phase flow within a rock mass, where both air and water phases flow together, the accurate flow measurement of each individual phase is important in numerical analyses. The increased quantity of water phase decreases the relative permeability of the air phase, and vice versa. The relative permeability is important to analyse the risk of groundwater inundation and gas outbursts particularly in underground excavations. Two-phase flow (i.e., water and air) behaviour through naturally and artificially fractured standard rock cores is investigated using the high-pressure triaxial equipment developed by the authors. Findings of this study show that the individual flow rate components of two-phase flow linearly increase with the increase in inlet fluid pressure, which suggests the applicability of a modified DarcyÕs law, using the relative permeability factor, in unsaturated flow. When the relative permeability of one phase increases, the relative permeability of the other phase decreases. The flow rate decreases with the increase in confining stress for both single and two-phase flow situations. However, this reduction of flow rate becomes marginal, once the confining stress is exceeded above a certain value.