The mechanical properties of cementitious composites subjected to carbonation curing depend on the carbonation degree, which is influenced by the diffusion of CO2 within the cementitious matrix. It has been found that due to the decrease in CO2 diffusivity as the curing progresses, the carbonation hardening is not uniform across the cross-section of the composite. The non-uniform carbonation of the cementitious matrix is expected to significantly influence the fiber-matrix interaction in fiber-reinforced composites (FRCs) subjected to carbonation curing. This study aims to understand the effects of carbonation curing regimes on the fiber-matrix interfacial properties. Single fiber pullout tests using polyvinyl alcohol (PVA) fibers embedded in reactive magnesia cement (MgO) matrix were conducted to determine the chemical bond, frictional bond, and slip hardening parameters. Three different curing conditions – 10% CO2, 0.5% CO2, and ambient curing (i.e., 0% CO2) were investigated. Results showed that the chemical bond between the fiber and matrix is higher when subjected to carbonation than ambient curing for oil-coated fiber, whereas non-coated fiber showed reduction in chemical bond when subjected to carbonation. The fiber-matrix frictional bond increased with the increase in CO2 concentration. The effect of CO2 concentration on slip hardening was negligible. These experimental results will aid in modifying the fiber-bridging analytical models to account for the non-uniform carbonate hardening of the cementitious matrix in FRCs.