Abstract： Objective To investigate the role of apoptosis in the remodeling of temporomandibular ioint(TMJ)under pressure.nethods Synovial fibroblaslt obtained from rat temporomandibular joint were subiected to different hydrostatic pressure for 12 h. Changes of uhrastmeture were observed by transmission electron microscope.Results At 30 kPa,the uhlastructure of synovial fibroblasit showed no obvious changes.At 60 kPa.the chromatin was condensated,the karyon took on crescent and the mitochondria seemed varicose.At 90 kPa,the apoptosis-like body was wrapped by membrane and embedded in the high density chromatin.Condusions Apoptosis-like change took place in ultrastructure of synodal fibroblasts under hydrostatic pressure,and the degree of the change was related to the hydrostatic pressure exerted.