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The carbonation of lime-treated soils that occurs during the short-term and long-term curing is not sufficiently explored in the domain of lime stabilization. The present study investigates the carbonation mechanism in lime-treated silty clay treated with two lime contents (4%, 8%) subjected to different curing periods (7, 90, 180, and 365 days). The cured samples were exposed to accelerated carbonation, and subsequent change in the unconfined compressive strength was compared with that of control samples tested under a nitrogen environment. The extent of carbonation was measured using phenolphthalein solution. X-ray diffraction technique and thermogravimetric analysis were used to analyze the reaction products resulted from carbonation. The morphology of carbonates and effects of carbonation on the pore structure were assessed using a scanning electron microscope and mercury intrusion porosimeter, respectively. Results show that carbonation has a deleterious effect on the performance of lime-treated clay. The strength of lime-treated soils upon carbonation decreased by 30% on average. The fabric structure of treated clay was found to vary with lime content and curing period, which determined the extent of carbonation. Decalcification of reaction products and cracking induced by the carbonation of residual lime contributed to the reduction in compressive strength of treated clay. The observed strength behavior of the carbonated samples is substantiated by quantifying the variation in pore structure characteristics.