This study aims to investigate the relationship between levels of fluid intelligence and higher-order thinking skills according to Bloom's three levels classification (analysis, evaluation, creation) among sixth grade students in Jordan in the subject of work and energy as one of the science book topics for the first semester of the academic year 2021-2022. For this purpose, a test for higher-order thinking skills was designed on the subject of work and energy, consisting of 17 paragraphs of the type of essay questions and multiple-choice in the 3 areas of higher-order thinking skills (analysis, evaluation, creation). The standard Raven test of fluid intelligence with its 5 levels was also applied to the students. After conducting the statistical analysis, the results of the study revealed: (1) a decrease in the level of higher-order thinking skills to less than the average (analysis, evaluation, and creation, respectively); and (2) a positive correlation between the students' fluid intelligence and their scores in the higher-order thinking skills test. Therefore, the study recommended including activities that take into account fluid intelligence in the curricula to improve students' performance in higher-order thinking skills.