The purposes of this research were: 1) to compare critical thinking abilities before and after learning by using problem-based learning management; 2) to compare students ability to think critically before and after school by managing learning according to the teacher’s manual; 3) to compare students ability to think critically after learning during the management of learning by using problem-based learning and learning management according to the teachers manual; 4) to compare the academic achievement after studying between learning management based on problem-based learning and learning management according to the teachers manual. The sample of this research was a group of 50 Mathayomsuksa 3 students from Matthayomwatkhaosukim School in Tha Mai District, Chanthaburi Province in academic year 2018. The instruments were a critical thinking skill and learning achievement test in Citizenship in Democracy using problem-based learning and the teachers manual of Mathayomsuksa 3 students. The reliability of the critical thinking ability test was 0.86 and the reliability of achievement test was 0.88. The statistics used for data analysis include mean and standard deviation.