The purpose of this study was to investigate the marginal adaptation and microleakage of SonicFill composite with different photopolymerization techniques. Class II cavities were prepared in 40 premolars and divided into groups according to the photopolymerization technique (n = 10): G1:1200 mW/cm for 20 s; G2:1200 mW/cm for 40 s; G3:Soft-start with 650 mW/cm for 5 s and 1200 mW/cm for 15 s; G4:Soft-start with 650 mW/cm for 10 s and 1200 mW/cm for 30 s. The cavities were restored with OptiBond FL adhesive and SonicFill. Epoxy resin replicas were obtained before and after thermocycling. The occlusal and cervical margins were analyzed with scanning electron microcopy and expressed as the percentage of continuous margins (%CM). The specimens were submitted to microleakage with silver nitrate. ANOVA and Tukey's test revealed that the %CM at the linguo-occlusal margin for group 1 (83.19%) was significantly different from groups 2, 3 and 4, which had values over 95%. At the cervical margin, there was no statistically significant difference between the groups. After thermocycling, there was a significant decrease in %CM. The predominant score of microleakage was 1 in enamel and 3 in dentin. The SonicFill composite led to gap formation and microleakage, especially in the dentin at the cervical margin, regardless of the photopolymerization technique employed.