Dentofacial growth interferences, caused by abnormal lip and tongue function in the mixed dentition period are a common clinical condition. The main purpose of the treatment in such cases is to eliminate oral dysfunction, establish muscular balance and correct or diminish maxillary incisor protrusion. The position of the teeth is determined by the lip and tongue pressure. Lip function may have been the cause of forcing teeth in to malposition they occupy. The case report is presented where the myofunctional trainer T4K is used during growth phase. How to cite this article Tripathi NB, Patil SN. Treatment of Class II Division 1 Malocclusion with Myofunctional Trainer System in Early Mixed Dentition Period: J Contemp Dent Pract 2011;12(6):497-500.