The purpose of this study was to investigate the effects of 5E inquiry learning activities on students' achievement, attitude toward chemistry. A non-equivalent control group design was used to the quasi-experimental research in this study. A total of 34 (8 males and 26 females) undergraduates in Turkey voluntarily participated in the study. The 5E Inquiry Learning Activities were applied to the experimental group and lecture-based traditional activities were applied to the control group. The both two groups were taught by the same instructor and used same books. The Chemical Equilibrium Concept Test (CECT) and the Attitude toward the Subject of Chemistry Inventory (ASCI) were applied to both groups as pre-test and post-test. The results of the study revealed that 5E inquiry learning activities were more effective in improving the achievement in chemical equilibrium compared to lecture-based traditional activities. In addition, the results showed that there was no statistically significant mean difference between experimental and control groups with respect to attitude toward chemistry.