The aim of this study was to investigate the effect of 5E learning cycle instructional model using socioscientific issues (SSI) learning context on students\u27 critical thinking skills of acid-base. This study used quasi-experimental posttest only control group design. The sample consisted of three classes, which were XI MIA-4class (n = 32) that learned using 5E LC model, XI MIA-5 class (n = 33) that learned using 5E LC+SSI, and XI MIA-6 class (n = 32) that learned using conventional method. The samples were choosen by convenience sampling technique. The test instrument consisted of 15 multiple choice items which were valid and reliable (r = 0.806). The data were analyzed using one way ANOVA test and LSD posthoc test. The results of this study indicated that the students who learned using 5E LC+SSI model showed greater levels of critical thinking skills ( = 74,95) than both the student who learned using 5E LC model ( = 74,17) and the student who learned using conventional method ( = 68,96). Based on statistics analysis, there was significant differences on students\u27 critical thinkings between students taught using conventional method and students taught either using 5E LC+SSI model and 5E LC model. However, there was no significant differences on students\u27 critical thinking skills between students taught using 5E LC+SSI model and the students taught using 5E LC model
