Since early Orthodontics, one of the main concerns is to correct Skeletal Class II. For this Purpose they designed different functional appliances, and performed many cephalometric studies to evaluate treatment results for these appliances on dentofacial complex. Our clinical experience, show the ability of treatment of preadolescents by advancement the mandible in skeletal class II correction with Sliding Plates. and for this purpose, lateral cephalometric study was performed to evaluate treatment results at dentofacial complex. 19 preadolescents ages 11-14 years with skeletal class II and mandibular retrognathism Sliding Plates consist of two separated removable parts, the upper one has midpalatal expansion and vertical wire, the lower is provided with anterior bite plane. The plates were used for 6-12 months. Lateral cephalograms were taken before treatment and immediately after treatment. The results after treatment were compared with the pretreatment measurements before treatment. After treatment, advancement of the mandible and the parts of TMJ has been observed. Thus, the use of sliding plates are useful to correct skeletal class II with mandibular retrognathism, especially in cases associated with narrow upper dental arch for children their ages do not permit the use of pre-functional preparation, and additionally, in cases that require functional rehabilitations.