CO2 capture and geological sequestration is one of the most practical and efficient methods of mitigating anthropogenic CO2 emissions. Due to the uncertainties associated with CO2 injection into deep saline reservoirs, the interaction between the host rock and the injected CO2 needs to be better understood as it can lead to considerable pore-structure changes. The geochemical reactions, especially mineral dissolution, can compromise the mechanical properties of the reservoir rock, which consequently threatens the reservoir stability and integrity. Therefore, it is crucial to capture the variation of mechanical properties of the reservoir rock upon CO2 injection. In this study the variation of elastic properties (e.g. Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio) of a brine-saturated sandstone specimen upon injecting CO2-enriched brine is investigated. The elastic properties of the specimen were initially characterized through multi-stage elastic (MSE) test before injecting the CO2-enriched brine. Then, the synthetic brine solution was enriched with CO2 and injected into the brine saturated sandstone specimen. The mechanical test results revealed that a significant mechanical weakening occurred upon injecting CO2-enriched brine into the sandstone specimen. This mechanical degradation can be attributed to the dissolution of calcite and clay minerals. The results from this study indicated that the mechanical deterioration of reservoir rock during CO2 injection should be considered through the entire CO2 sequestration process (i.e. site selection, injection operation, and post-injection monitoring).