Objectives : The purpose of this study was to examine the knowledge of orthodontic patients about oral health knowledge and their actual oral hygiene care, which affected the oral hygiene of orthodontic patients. It's specifically meant to provide information on the prevention of the possible side effects of orthodontic treatment and the promotion of the oral health of orthodontic patients. Methods : This study were 227 orthodontic patients of dental clinics specialized in orthodontics. The collected data were analyzed by the statistical package SPSS WIN 18.0. Results : 1.As for Oral health knowledge, they had the best knowledge about smoking and dental checkup among the subfactors of oral health knowledge. 2. As to actual oral hygiene care, what they did best was doing toothbrushing before sleeping and what they did worst was avoiding eating food injurious to teeth. 3. They scored highest in the right toothbrushing(3.85), the use of oral hygiene supplies(3.62), the prevention of periodontal diseases(3.13) in the subfactors of actual oral hygiene care. They scored lowest in dental checkup and diet(2.99). 4. There were significant differences among the patients in oral health knowledge according to age(F=2.95, p<.05). Those who received another treatment during orthodontic treatment had a better oral health knowledge than the others who didn't, and the gap between the two was statistically significant(t=2.26, p<.05). 5. There were differences among the patients in actual health hygiene care according to gender(t=2.71, p<.01), age(F=4.40, p<.01), educational experiences about oral hygiene care(t=3.06, p<.01) and experience of receiving another treatment during orthodontic treatment(t=2.56, p<.05). 6. There was a positive correlation between oral health knowledge and oral hygiene care(r=.261, p<.001). Conclusions :The above-mentioned findings suggest that more education of diet and toothbrushing should be provided for orthodontic patients to improve their oral health care.