─ All of educational process referring to 21 st century educational purpose, and having a cooperative skill is one of them. This has increased the need of learning method that could improve children's cooperative skills. In this research, we implement project-based learning on 44 children (5-6 years old) of Al-Hikmah Kindergarten learning process to improve their cooperative skills. This experiment uses nonequivalent control group design and divided into three phases, which are pretest, treatment, and posttest that happened for 5 weeks. Observation sheets used for measuring children's cooperative skills. Analysis data technique that used are quantitative. Comparison between children's cooperative skills before and after implementation done by paired sample t-test using SPSS 16.0 for Windows. The result of paired sample t-test shows that there is a significant improve on children's cooperative skills by using project-based learning. Based on the data, we conclude that project-based learning could improve children's cooperative skills.