Objectives:The aim of the present study was to evaluate the effect of two lining procedures on the marginal integrity of compound posterior direct resin composite restoration Materials And Methods:Forty two freshly extracted maxillary human premolars were selected and randomly divided into three groups (n=14) according to the liner used either no liner control group (A1); self adhesive flowable composite SAFC (A2) or resin modified glass ionomer liner RMGI (A3). Each group was subdivided into two subgroups (7 each) according to the testing periods either 24h after composite placement (B1) or three months later (B2).Standardized classes II cavity wereprepared to be 3mm at the occlusal portion and 4 mm at the proximal portion while the buccco-lingual width was 4mm.Five specimens of each subgroup were tested for microleakage by dye penetration method and two specimens were evaluated using scanning electron microscope SEM. After mechanical cycling loading.The specimens were immersed in 0.5% red fuschin for 24 hours. Dye penetration was detected using a sectioning technique. Results:The results showed that for control and self adhesive flowable composite liner materials showed 100% of the samples with grade 0, while resin modified glass ionomer liner revealed 80 % of the leakage with grade 0, 20 % of samples showed grade 1 (dye penetration up to one third of gingival floor), and there were no recording for leakage scores (2, 3 or 4). Both 24h and three months subgroups showed 93.3 % grade 0, 6.7 % was shown with grade 1, 0% of samples showed any other grades of leakage (2, 3 or 4).Conclusion:Lining of cavities with self adhesive flowable composite is a choice when sealing ability is a prime goal if compared to resin modified glass ionomer liner.