Background and Aims Accurate assessment of cardiorespiratory function, muscular strength, and endurance seems necessary to be aware of, provide exercise interventions, and prevent subsequent diseases. Therefore, the current research aimed to develop a comprehensive tool for assessing cardiorespiratory, muscular strength, and endurance function in people with intellectual disabilities. Methods The current research is fundamental and practical in terms of purpose. In this study, the psychometrics of 51 specific intellectual disability tests were used to develop a tool for measuring cardiorespiratory function, muscular strength, and endurance. The face validity of the instrument through a 51-test questionnaire by 15 experts and 15 intellectually disabled educators, the content validity through a 51-test questionnaire by 15 experts, and the construct validity through a 19-test questionnaire by 243 intellectually disabled educators were examined. The tool’s reliability was checked through internal, intra-rater, and inter-rater consistency. Internal consistency was estimated by calculating the Cronbach alpha. The intra-rater and inter-rater reliabilities were also checked through the implementation of the tests by 18 people with intellectual disability in three time points and with three raters through the internal correlation index (ICC), confidence interval (CI), and standard error of measurement (SEM). Data analysis was done through exploratory and confirmatory factor analysis with AMOS version 26 and SPSS software, version 22. Results Based on the content validity ratio (CVR) estimation, 19 out of 51 tests had a content validity ratio higher than 0.49, and the rest were excluded. Regarding construct validity, 10 out of 19 tests were removed, and the final 9 tests were approved for evaluating cardiorespiratory function, muscular strength, and endurance. Exploratory factor analysis extracted three latent factors that explained 46.21% of the total variance. Confirmatory factor analysis confirmed the final construct model. The factor analysis results included KMO=0.829 and BT=4706.93 (P<0.0001). Conclusion The current study provided a special set of tests for people with intellectual disability regarding cardiorespiratory assessment (one test), strength (four tests), and muscular endurance (four tests) after psychometry of 51 specific tests. By using this set of tests, it is possible to make an accurate assessment of the physical fitness of the health of people with intellectual disability.