Objective: Objective: To evaluate cuspal deflection and microleakage of complex class II cavities filled with bulk fill and incremental resin composite. Also, asses effect of water storage on microleakage. Materials and methods: 120 maxillary premolars were collected, prepared into  standardized (MOD) cavities, then teeth were divided   as the following:-  Forty tooth of the 120 prepared teeth  were randomly assigned for cuspal deflection test which were randomly divided into four groups (n=10)  according to restorative materials used  (Filtek z350,Filtek bulk fill, Fill-up bulk fill , Beautifil bulk fill). The remaining 80 tooth were used for microleakage test, randomly divided into four groups (n=20) according to the previous mentioned used restorative materials. Results: For the cuspal deflection test, A statistically significant difference was found between bulk-fill and incremental-fill composite. Concerning microleakage results, no statistical significant difference was found between all groups investigated immediately or after water storage. Conclusion: Bulk fill resin composites had reduced cuspal deflection than incremental composite with no difference in microleakage recorded.