This study aimed to identify the degree of knowledge efficiency of physical education teachers in health-related fitness, and to recognize the differences in the degree of knowledge efficiency depending on different variables (educational qualification, number of years of experience). The study sample consisted of (59 randomly-selected teachers) of physical education teachers in the elementary grade schools in Jeddah. The sample represents 13.1% of the study population. The researcher used the descriptive style survey, using a questionnaire as a tool for all data collection. The questionnaire consisted of (36) items distributed among three areas (cognitive domain, the applied field, the educational awareness field). Data were statistically analyzed using the Statistical Package (SPSS) program to get the results using averages, standard deviations, and ranks, and analysis of variance. The study results showed that the degree of knowledge efficiency of physical education teachers in all areas of the study came at a high level, as the results came in the cognitive domain at a very high level, while came at a high level in the applied field and the field of educational awareness. The results also showed no statistically significant differences in the degree of knowledge efficiency of physical education teachers due to the study variables (educational qualification or number of years of experience). The researcher recommends to increase the attention paid to the applied research and awareness educational awareness for physical education teachers in fitness related to health, and attention to training during the service of the physical education teachers by conducting more training courses and workshops in the health-related fitness. The researcher also recommends to conduct further scientific studies on knowledge efficiency of physical education teachers in physical health-related fitness at different school grades and geographic areas.