Although the development of critical thinking and chemical literacy is a major goal of science education, the adequate emphasis has not been given to the measurement of both skills. This study reports the development and validation of an integrated assessment instrument to measure students' critical thinking skill and chemical literacy together in chemical equilibrium. The development of the framework in this study was implemented based on 4-D model. The stage of development begins with define, design, develop, and disseminate. The initial integrated assessment consisted of 37 open-ended two-tier multiple-choice question items. The preliminary version of the integrated assessment was initially piloted on review with experts and the paper-pencil test was administered to a group of students. The data were analyzed using Item Response Theory (IRT). Analysis factor was involved to find out the construct validity and strengthen the finding of content validity with the experts. In additionally, PCM 1-PL model was conducted to examine the quality of parameter estimates of the test items. The findings of the content validity, construct validity and quality of the items, overall suggest that the integrated assessment has relatively high validity and reliability and can be used for measuring the 13 integrated skills can be measured in chemical equilibrium.