Determination of rock mass mechanical properties plays vital role in design and construction of tunnels in rocks. This paper presents the estimation of rock mass parameters using intact rock parameters. Rock mass parameters are generally determined from unconfined compressive strength values of intact rock samples and other index parameters like geological strength index (GSI), rock mass rating (RMR) etc. The mechanical properties of rock masses were obtained using a computer program Roclab based on Hoek-Brown Failure criterion which yield values of strength (compression and tension), deformation modulus and shear strength parameters of the rock mass. The input parameters GSI is used in conjunction with unconfined compressive strength (UCS) of the intact rock (σci) and the material constant (mi). Further, the variation of rock mass parameters with the intact rock parameters has been developed for the different disturbance factor varying 0-1. It has been observed that all the parameters significantly affect the rock mass parameters hence need to be considered judiciously for evolving reliable design rock mass parameters.