The purpose of this stdudy were to test the effects of de Bono\'s CoRT Thinking Program on the creative thinking and the changes of thinking styles. Two sectons of CoRT Thinking Program(CoRT 1 & CoRT 4) were used in this study. And the dependent cariables were 4 creative thinking skills(fluency, flexivility, originality, & elaboration) and 5 thinking styles(synthesist, idealist, pragmatist, analyst, & realist). Subjects of this study were high school students. Numbers of scbject in experimental group were volunteers. And the experimental group was participated in the CoRT ! & CoRT 4 lessons during 8 months. During experimental period, total instruction time was 20 hours. The finkings of this stduy are as follws. 1. de Bono\'s CoRT 1 & 4 Programs has a significant increasing effects on the 4 creative thinking skills. Also CoRT Thinking Programs has an clear effect of developing the positive attitude to the problem - solving situation. 2. de Bono\'s CoRT 1 & 4 Programs has not clear effects on the changes of students\' thinking styles. On the basis of the above results, the follwing recommendations for the future research are proposed. 1. Although de Bono\'s CoRT Thinking Programs have the obvious effects on the creativity of the subjects, the transfer effects to real-life situations must be examined throuhgly. 2. Future researchers should test the validity of Harrison & Bramson\'s Thinking Styles Test in terms of individual differences of personality types such as MBTI.