The average thinking skills of chitis in elementary school students are still relatively low, this can be seen during integrated thematic learning. To overcome these problems, LKPD will be developed based on Project Based learning (PjBL). This study aims to: 1) develop PjBL-based LKPD that is feasible to be used to improve students' critical thinking skills in integrated thematic learning in grade IV, 2) Analyze the effectiveness of PjBL-based LKPD in improving students' critical thinking skills in integrated thematic learning in Class IV. This research is a Research and Development research. Sampling using purposive sampling technique. The population in this study was grade IV students of SD Negeri 2 Pinang Jaya Kemiling Bandarlampung. Data collection using documentation techniques, written tests, and questionnaire dissemination. The instrument used is a test that has been tested for validity and reliability using the help of the SPSS 24.0 for windows program with a significance level of 0.05. Furthermore, the data is processed using an independent sample-test. The research results are (1) PjBL-based LKPD are suitable for use and (2) PjBL-based LKPD are effective for use.