In-situ permeability of rock mass is governed by its discontinuities and is important to investigate it by a widely accepted parameter, “rock quality designation (RQD)”. In this regard, site investigations conducted during construction of hydraulic structures in the complex lithological units of Oman were reviewed with aim to summarize the data obtained by drilling of boreholes with recovered cores (RQD) and Lugeon's tests (in-situ permeability) in discontinuous sedimentary rocks. The plot of RQD and apparent in-situ permeability suggested a consistent relationship, with respect to the each lithological unit and extent of investigation as well. The developed relationship is recommended for the onsite determination of apparent in-situ permeability K_a of discontinuous sedimentary rocks by recovering the RQD values only. However, the RQD being less than the threshold value of 25% necessitates a detailed investigation to elucidate the in-situ permeability.