A series of unconfined compression tests (UCTs) were conducted to investigate the effects of content of reactive magnesia (MgO) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive MgO treated silt soils. The soils treated with reactive MgO at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive MgO content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive MgO content, the unconfined compressive strength (qu) increases at a given carbonation time (＜10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive MgO exists at approximately 25% and a critical carbonation time exists at about 10 h for the development ofqu. A simple yet practical strength-prediction model, by taking into account two variables of reactive MgO content and carbonation time, is proposed to estimatequ of carbonated reactive MgO treated soils. A comparison of the predicated values of qu with the measured ones indicates that the proposed model has satisfactory accuracy.