Background: This study aimed to compare the efficacy of the snowplow, open sandwich with resin-modified glass ionomer (RMGI), and flowable composite liner techniques for the reduction of cervical microleakage of posterior Class II composite restorations. Materials and Methods: In this in vitro study, 60 class II cavities were prepared in 30 sound extracted premolars. The gingival floor of the cavities was placed 1 mm below the dentin-enamel junction. The teeth were randomly assigned to four groups (n=15). The enamel margin was etched, and SE Bond was applied. The teeth were restored with x-tra fil in group 1 (control), x-tra base + x-tra fil (snowplow technique) in group 2, RMGI + x-tra fil (open sandwich technique) in group 3, and x-tra fil + x-tra base (flowable composite liner) in group 4. After thermocycling, the teeth were immersed in 2% Fuchsin for 24 hours, and were then sectioned. Cervical microleakage of restorations was scored under a stereomicroscope at 20X magnification, and analyzed using the Kruskal-Wallis and Mann-Whitney tests (α=0. 05). Results: The microleakage of the snowplow (P<0. 001), open sandwich (P=0. 003), and flowable composite liner (P=0. 05) groups were significantly higher than that of the control group. The microleakage of the snowplow technique was also significantly higher than that of the flowable composite liner (P=0. 047). No other significant differences were found (P>0. 05). Conclusion: Within the study limitations, the results indicated that the snowplow, open sandwich with RMGI, and flowable composite liner techniques were not effective in reducing cervical microleakage of class II composite restorations.