Objective: To evaluate the adaptation of different materials for gingival layer in Class Ⅱ restorations using Micro-CT.  Methods: Eighteen extracted human premolars were selected, and Class Ⅱ cavities were prepared. The teeth were randomly divided into six groups and restored using layering technique. Six materials were used for gingival layer, including four injectable materials: Beautifil Flow Plus F00 (F00), Beautifil Flow F10 (F10), Filtek Z350 Flowable (Z350F), FujiⅡ LC CAPSULE (Fuji), and two packable materials: BeautifilⅡ (BF), Filtek Z350 (Z350). The restored teeth were scanned with micro-CT and the images were 3D reconstructed to evaluate the volumes and the distribution of the voids on the restorationtooth interface of the gingival layer. The volume of the voids were statistically analyzed using nonparametric Jonckheere-Terpstra tests. Results: The volumes (mm3) of the voids on the restorationtooth interface were: Z350F (0.000 15), F10 (0.000 39), F00 (0.012), Fuji (0.070), Z350 (0.16) and BF (0.20). There were significant differences between Z350F/F10 and Fuji/Z350/BF (P<0.05). Most of the voids were found on the point-line angles of the cavities. Conclusion: The voids on the restoration-tooth interface were mainly on the point-line angles of the cavities. Injectable materials with high flowablility could reduce the restorationtooth interface voids significantly when used for the gingival layer in Class Ⅱ restorations.