Background: The context-based approach (CBA) is one of the approaches that allow learning to take place with real and related context, and this has increasingly become more popular. Purpose: The purpose of this study is to investigate the effect of the REACT strategy of the CBA on remedying 12th grade students' alternative conceptions of "alkenes" and improving their conceptual understanding. Sample: The sample of the study consisted of 20 (10 girls and 10 boys--aged 17 to 18 years) 12th grade students who enrolled in the Chemistry course in the 2014-2015 academic year in a public high school. Design and methods: Since the current study evaluated student gains in conceptual understanding by means of a pre-test, post-test, and delayed-test scores, the study used a single group pre-posttest research design. To gather data, an Alkenes Concept Test (ACT) with 15 multiple choice items and a semi-structured interview protocol with 4 open-ended questions were used. The ACT was administered before and after the intervention as pre- and post-tests. Then, the semi-structured interview protocol was carried out. The ACT was re-administered third time to the students as a delayed-test one month after the intervention. Results: The results showed that the REACT strategy was effective to remedy the alternative conceptions and helped students to keep new conceptions in their long-term memory one month after the implementation. Conclusions: The REACT strategy was effective in enhancing conceptual understanding of "alkenes" and helping 12th grade students to link between the scientific concepts and daily life.