The influence of carbon dioxide (CO2) curing on the compressive strength of oil shale ash (OSA) concrete as partial cement replacement was investigated. 15 cm cubes with a 30 replacement percentage were tested after seven days of conventional curing and carbonation curing at 4 bar CO2 pressure. Research results demonstrate that CO2 curing influences the compressive strength of concrete significantly. There is a linear relationship between CO2 pressure and the duration of curing, as well as the compressive strength of OSA-based concrete. A sample of ordinary Portland cement was used as the control sample. The replacement of 30 cement by OSA increased the 7-day compressive strength from 48.5 to 55.5 MPa for plain cement samples and from 36.5 to 42.3 MPa for ash-based samples. From a technical standpoint, OSA-based concrete carbonation curing is still too immature for widespread application. Nonetheless, it is continuously developing in response to greenhouse gas reduction and paving the path for a more sustainable construction materials business. © 2024, Institute of Technology PETRONAS Sdn Bhd.