This study was carried out to research the adaptation patterns of head posture after activator therapy in functional class ill malocclusion patients. For this purpose, 29 functional class III malocclusion patients, from the ages of 8 to 13 years old, were used. 1. Increase in capacity of oral cavity capacity were found in all the samples, but craniocervical angulation were varied into increased group and decreased group after activator therapy. 2. Head posture exhibited the compensatory adaptation in the relative growth increments of the vertical dimension, ALFH and PLFH. 1) A group with more PLFH and less sagittal angle showed relatively small growth increment in PLFH during the treatment period, thus craniocervical angulation was increased. 2) A group with less PLFH and more sagittal angle showed relatively great growth incrmenet in PLFH during the treatment period, thus craniocervical angulation was decreased.