Orthodontic tooth movement requires remodelling of periodontal tissues, especially alveolar bone. Fluoride is known to be a potent inhibitor of osteoclastic bone resorption. The purpose of this study was to examine the effects of a consumption of fluoride on osteoclast numbers appearing on the pressure side of alveolar bones at experimental tooth movement. 40 male rats were exposed to 0, 10, 25 mg/kg/day of sodium fluoride(NaF) in their drinking water for up to 60 days. Orthodontic appliance were activated to mesially tip maxillary first molar with 50- 70g. The rats were sacrificed at 1, 2, 4 days after initial activation, The number of osteoclast was counted in a 450 X 700μm² area interradicular septum on the pressure side of the maxillary first molar. The results were as follows, 1. There was significantly different osteoclast number between control group and 25 mg/kg/day group at all measured time. (p< 0.05) 2. There was significantly different active bone-resorption area between control group and 25 mg/kg/day group except at 96 hours post activation. (p< 0.05) 3. There was slight reduction of active bone- resorption area in control group from 48 hours to 96 hours but in both 10 mg/kg/day group and 25 mg/kg/day group a slight increase was observed from 48 hours to 96 hours.