Vitamin D deficiency is prevailing in Saudi Arabia. Recent national data indicated an inverse association between vitamin D status and coronary heart disease (CHD), which increases concerns about vitamin D deficiency as a serious public health problem. Therefore, the current study aimed to Assessment Knowledge regarding Vitamin D deficiency among female adult attending the Primary Health clinic at Makkah, Saudi Arabia, 2021. Saudi Arabia has one of the highest reported incidence of vitamin D deficiency in studies conducted worldwide. However, there has been very limited exploration of vitamin D related knowledge, attitudes and practices among female adult in Saudi Arabia. However, the case of vitamin deficiency is reported to increase in many female Saudi Arabia worldwide, especially in Saudi Arabia. Mothers, having adequate knowledge about vitamin D and its supplementation, may lead to possible lowering of the cases of vitamin D deficiency and its complications.Ami of the study: To assessmentKnowledge regarding Vitamin D deficiency among female adult attending the Primary Health clinic atMakkah, Saudi Arabia, 2021 Methods: This was an analytical cross-sectional study conducted during 2021,among female adult attending the Primary Health clinic atMakkahAL-Mokarramahrandom samplingtechnique was applied and an Arabic self-administered questionnaire used for data collection.Result:shows that most of the participants (37.0%) were in the age 25-30 years also regarding level of education the majority of participant are Secondary educationwere(34.0%). regarding Marital status the majority of participant are married were(58.0%). Regarding the Economic level the majority of participant Averagewere(45.0%). Regarding the Chronic diseasethe majority of participant No.were(72.0%). Conclusion:The low levels of knowledge about vitamin D and low consumption of vitamin supplementation, including vitamin D, calcium, multivitamin, and calcium supplements with vitamin D, may have contributed to the higher prevalence of vitamin D deficiency among the female adult. Further studies using a qualitative approach are crucial to explore the underlying reasons for low knowledge about vitamin D and behaviors related to vitamin D including the intake of vitamin supplementation that may contribute to the high burden of vitamin D deficiency in the country.