To reduce the emission of CO2 into the atmosphere, it is proposed to store CO2 into deep coalbeds which may also enhance the production of naturally-stored methane from coal formations. Many studies have been reported investigating the effect of CO2 injection on the flow properties to provide a means of estimating the recoverable CH4 and storable CO2. However, assessment of the long-term integrity of stored CO2 and the potentially damaging effects of CO2 on the mechanical response of coal have been largely neglected. Understanding the geomechanical response of coalbeds to CO2 injection can be crucial in site selection, in designing and planning coalbed geosequestration operations. To investigate the effects of CO2 adsorption on the mechanical strength and stiffness of coal specimens, a series of triaxial experiments have been undertaken. Over 40 core specimens of Australian black coal from the Sydney Basin have been tested. The behaviour of water-saturated and CO2 saturated specimens have been investigated at confining pressures up to 5.5 MPa at room temperature. Results showed that the strength and stiffness of CO2 saturated specimens are significantly less than those of water saturated specimens.