This study was conducted to investigate the effectiveness of learning activities based on case-based learning over traditionally designed chemistry instruction on eleventh grade students' understanding of solubility equilibrium. The subjects of this study consisted of 63 eleventh grade students from two intact classes of an urban high school instructed with same chemistry teacher. Each teaching method was randomly assigned as control and experimental group. The experimental group received case-based learning, in which real life cases were discussed via small group discussions; the control group received traditional instruction in which lecturing and discussion was carried out. The results showed that case-based learning instruction produced significantly greater achievement in understanding of solubility equilibrium concepts in comparison with traditional instruction. Also, the results revealed that students had misconceptions related to chemical equilibrium. According to the results of this study, case-based learning is effective for elimination of misconceptions and the enhancement of students' understanding.