This study investigates the effect of a conceptual change approach over traditional instruction on students' understanding of chemical equilibrium concepts (e.g. dynamic nature of equilibrium, definition of equilibrium constant, heterogeneous equilibrium, qualitative interpreting of equilibrium constant, changing the reaction conditions). This study consisted of 85 undergraduate students from two classes enrolled on an introductory chemistry course. One of the classes was assigned randomly to the control group, and the other class was assigned randomly to the experimental group. During teaching of the topic of chemical equilibrium concepts in the chemistry curriculum, the conceptual change approach was applied in the experimental group whereas "traditional instruction" was followed in the control group. The data were analyzed using analysis of covariance. The results showed that the students in the experimental group performed better compared to the control group. The average percent of correct responses of the experimental group was 70%, and that of the control group was 51%, after treatment. In addition, it was found that students' science process skills made a statistically significant contribution to the variation in students' understanding of chemical equilibrium concepts. (Contains 3 figures and 5 tables.)