This study has been carried out to determine the effectiveness of case-based learning related to reaction rate on students' conceptual understanding and conceptual change. In this respect, a class of 11 th grade students in an Anatolian High School in the center of Izmir city was chosen randomly as experimental group (n=26) and another as control group (n=22). Reaction rate unit was taught to the experimental group within case-based learning method, and to the control group through activities defined in Chemistry curriculum. Comprehension Test developed by Cakmakci (2005) was utilized as data collecting instrument. The Comprehension Test was applied simultaneously to both experimental and control groups before and after the teaching. The data collected via the Comprehension Test was analyzed in terms of both quantity and quality. As a result of the study, it was noted that there was a significant difference between the groups after the instruction in favor of the experimental group. Also, it was determined that case-based learning was more effective in promoting conceptual change and assuring higher level of conceptual understanding for students.