Objective: To evaluate, in vitro, dentin caries inhibition ability of a composite restoration with glass-ionomer liners in an open-sandwich configuration. Method and Materials: Rectangular dentin cavities (n = 5) were restored with a composite and glass-ionomer liner in an open-sandwich configuration where the liner was applied up to the cavity margin. Liners used were 3 resin-modified glass-ionomers (Vitrebond, 3M ESPE; Vitrebond Plus, 3M ESPE; Fuji Lining LC Paste Pak, GC) and a conventional glass-ionomer (Ketac Bond, 3M ESPE). The control group was a composite restoration (Filtek Z250, 3M ESPE) without a liner. Specimens were immersed in lactic acid gel for 3 weeks to create a demineralized lesion before being subjected to microradiographic analysis. The width of the area where the demineralization was completely inhibited at the restoration interface was measured. The total mineral loss (ΔZ) was determined at 0.25 and 1.0 mm from the cavity margin. Results: An inhibition zone was observed at the interface of all open-sandwich restorations but not in Filtek Z250. (ΔZ at 0.25 mm of all the open-sandwich restorations was significantly less than that of Filtek Z250 (analysis of variance, Scheffe's S, P .05). At 1.0 mm, only the open-sandwich restorations in Vitrebond and Vitrebond Plus groups had significantly less (ΔZ than Filtek Z250. Conclusion: Under an in vitro demineralization challenge, glass-ionomer liners in an open-sandwich restoration exhibited pronounced inhibition zones at the dentin margin and lowered the amount of mineral loss in the vicinity of 0.25 mm from the restoration interface. Keywords: demineralization, dentin, glass-ionomer liner, open-sandwich restoration