"The Science, Technology, Engineering, Art and Mathematics" (STEAM) approach is increasingly used as it is believed to be capable of facilitating students to understand subjects and adjust to the 21st century competency framework. Integrating a project-based learning (PjBL) model with STEAM is part of good teaching practice. The PjBL-STEAM learning is conducted online (e-learning) to facilitate students in accessing learning content due to the COVID-19 pandemic. The research analyzes the PjBeL-STEAM learning model on the improvement of students' concept mastery in ecological concepts. The learning emphasizes project activities by conducting an independent practicum and creating an animation of biogeochemical cycles. The research involves 72 students of Grade 10 in one of the senior high schools (SMA) in Jakarta. Instruments employed in the research include pretest and posttest of the mastery of ecological concepts. Data is analyzed using independent sample t-test. The research results indicate that the PjBeLSTEAM learning model improves students' mastery of ecological concepts. The research has a limitation related to the assessment of students' attitudes that is not conducted due to online learning.