The aim of this study was to investigate the effectiveness of case-based learning (CBL) over traditionally designed chemistry instruction (TDCI) on 10th grade students' perceived motivation about chemistry as a school subject. Two classes were randomly selected from a high school. One class was assigned to be an experimental group and the other was assigned as a control group. A total of 45 high school students from 10th grade were the participants of the study (25 experimental and 20 control group students). Students in the experimental group were taught by case-based instruction while the control group students received traditional instruction. Motivated Strategies for Learning Questionnaire (MSLQ) was administered to both groups of students as pre- and post-tests to measure their perceived motivation. The results of one-way MANOVA based on gain scores revealed that CBL was an effective method for promoting students' motivation towards chemistry. (Contains 4 tables.)