To analysis the effects of chincap therapy for early anterior crossbite and mandibular prognathism.136 patients anterior crossbite and mandibular prognathism aged from 3 to 14 years old at the start of treatment were treated with active chincap with bilateral force of 700 to 1000 gram. Every patient wore chin cap 12 to 14 hours daily, and most of those patients used removable appliances to open the crossbite of incisors. According to the age of patients, they were divided into four groups, C1 (3-5 years old), C2 (6-8 years old), C3 (9-11 years old) and C4 (12-14 years old). When the treatment ended after two years, we analyzed the models by measuring the length of maxillary on the models before and after treatment (U1 and U2 that's the distance between the tip of 1|1 and the distal plane of 6|6 or V|V and the overjet before and after treatment (L1 and L2). Then we calculated the obtained distance for the mandible related to the maxillary position X(X = (L2-L1)-(U2-U1)) and analyzed treating time and mandibular retreating speed in the four groups.The obtained distance for the mandible related to the maxillary position in C1, C2, C3 and C4 groups were 3.27 +/- 0.99 mm, 4.62 +/- 1.33 mm, 4.43 +/- 1.28 mm and 2.63 +/- 0.92 mm respectively, and the treating time in four groups were 8.92 +/- 2.66 months, 10.47 +/- 2.21 months, 13.07 +/- 2.00 months, 20.50 +/- 3.96 months respectively. The retreating speed of the mandible related to the maxillary position in the four groups were 0.37 mm/month, 0.44 mm/month, 0.34 mm/month and 0.13 mm/month respectively. The effects of the treatment in C1, C2 and C3 groups (3-11 years old) were remarkable, especially in C1 group (3-5 years old).The effects of chincap therapy for early anterior crossbite and mandibular prognathism were remarkable, especially for the very early crossbite patients.