Objectives : The purpose of the study is to investigate the knowledge and self care behaviors of orthodontic patients using clear aligner. Methods : A total of 181 orthodontic patients using clear aligner in Daegu filled out the self-reported questionnaire from September 6 to October 18, 2010. and 162 subjects completed orthodontic treatment. Results : There existed a significant difference in knowledge and self care behaviors between gender and wearing duration of clear aligner(p<0.01). Treatment duration influenced significantly on the score of self care behaviors(p<0.01) and the high score of self care behavior showed in short duration of treatment. Conclusions : Self care behaviors were closely correlated with treatment duration. An information for the clear aligner will be helpful to improve the knowledge and self care behaviors.