This descriptive study was done to investigate the critical thinking ability of senior nursing students in two types of nursing education programs: associate and baccalaureate programs. Data were convenently collected from 159 associate degree nursing(ADN)students and 158 baccalaureate degree nursing(BSN)students. All schools were the Ministry of Education accredited and located in Seoul City and Kyung gi Province. These data were collected by self reporting questionaire given over two months from March to May, 1995. The subjcets completed the Watson -Glaser Critical Thinking Appraisal (WGCTA)and a demographic questionnaire. The data was analyzed using descriptive statistics and t-test with the SAS program. The results of this study are as follows 1. The mean of critical thinking ability of the ADN students was 42.69. 2. The mean of critical thinking ability of the BSN students was 47.68. 3. There was significant difference in the WGCTA scores between the ADN and the BSN students (t=7.38 p<0.001) 4. This study suggests that critical thinking ability may increase with higher levels of nursing education. Possible explanations for these findings are discussed.