The aims of this study were to evaluate the microleakage in the Class II Cavities Restored with methacrylate resin composite (Tetric Ceram HB) or silorane resin composite (P90 Filtek) that had been stored in different situations and temperatures. Materials and Methods: thirty six intact human upper first premolars were employed. Two Class II cavities with specific dimensions had prepared on each tooth mesially and distally. Teeth were Restored by Methacrylate Resin (HB IVOCLAR), Silorane Resin (P90), Under three different conditions: Group (A): application of composite and Adhesive System at room temperature (24°C), Group (B): application of composite and Adhesive System, immediately after removal from refrigerator temperature (4°C), Group (C): application of composite and Adhesive System, 30 minutes after removal from the refrigerator at room temperature (24°C).Results: This study observed a statistically significant increase in microleakage when applying each of methacrylate composite (HB IVOCLAR) and silorane composite (P90) immediately after removal from refrigerator temperature (4°C) Compared when applied at room temperature (24°C) and when applied 30 minutes after removing from refrigerator temperature, no significant differences were found between silorane composite (P90) and Methacrylate composite (Tetric HB) in microleakage when comparing the two types of resin in the three ways used in storing both resins.