Rock strength parameters are vital to measuring the rock brittleness index in rock engineering for failure characteristics under geo-stress conditions, such as drillability of rocks, cutability assessment of sedimentary rocks and estimating fracture toughness. In addition, rock strength and brittleness index play a vital role in evaluating the stability of the surrounding rock mass in subsurface underground projects. This study aims to measure the rock strength parameters for brittleness index evaluation by conducting the uniaxial compressive strength (UCS) and tensile strength tests of sedimentary specimens. In this study, rock samples are collected from the anticline structure in the Chittagong hilly area, and experimental studies are conducted to measure UCS and tensile strength to obtain the brittleness index (BI) by following the standard procedures of the American Society for Testing and Materials. From the results, the measured UCS is very high and the tensile strength is relatively low with an average magnitude of 83.8 MPa and 1.65 MPa, respectively. Therefore, the BI is very high with an average value of 50.79. Hence, the BI indicates that the collected samples of the studied area are extremely brittle. The drilling performance for this rock is tough and the stability of the surrounding rock mass in the subsurface underground project is likely to fail due to the extremely high value of BI. These findings can be used to calculate the maximum and minimum wellbore fracture pressure regime for the wellbore failure analysis during drilling operations in geo-energy exploration phases.