This research is motivated by the importance of critical thinking skills in 21stcentury education. The purpose of this study is to determine the critical thinking skills of elementary school students and the factors that can influence it in Sukoharjo 02 Elementary School, Sukoharjo Regency. This study included descriptive qualitative research. The subjects of this study were class VI students who were selected by purposive sampling technique. Data collection is done through observation, interviews, and tests. Data analysis is done by flow analysis. Based on the results of research and discussion, information obtained from 6 of 28 students or about 21% of students whose grades can reach 70, the minimum completeness value 70. The average score of all students is 52. It shows that the students' ability to think critically is still low. Based on several indicators of critical thinking shows the average value of students answering interpretation questions, namely 46.43, analysis of 50.89, inference 65.18, and explanation 45.54. The low average value is caused by several factors, namely: students answer with short answers so the answers become incorrect, there are students' misconceptions because students' understanding from the beginning is wrong, and the most often done by the students is to answer systematically.