One of the successes of learning is the formation of thinking skills and understanding. Therefore in this study the formative assessment is implemented through Understanding by Design (UbD). The research objective is to find out the formation of understanding and to analyze the correlation between formative assessments and UbD. The study used quantitative method with a quasi-experimental design. Formative assessment strategies used were presentations, discussions, practicum learning, mind-mapping, and analyzing articles. The results of the study found that there was a significant increase in understanding after the implementation of formative assessment through UbD and a positive correlation between formative assessment and understanding. Formative assessment integrated into UbD is the originality of this research.