Background: Vitamin D deficiency is a pandemic especially in women in childbearing age mainly due to lack of awareness about the importance of vitamin D and prevention of its deficiency. Objective: To assess the knowledge, attitude and practice of mothers attending primary health care center in Cairo towards vitamin D, its supplementation & sun light exposure. Methods: A cross sectional study was conducted on 195 mothers attending a primary health care center in El-Sherouk city in Cairo using structured questionnaire including socio-demographic data, mother's knowledge, attitude and practice towards the importance of Vitamin D, its supplementation and sun light exposure for herself and her child and a scoring system was designed. Results: Less than one quarter of the mothers (22.6%) had a good knowledge (total knowledge score percentage > 50%). Thirty six percent (36%) of mothers had a positive attitude (total attitude score percentage ≥75%) & forty-six (46%) percent of mothers had a good practice (total practice score percentage ≥75%). About 53.5% of mothers were exposed to the sun from 10 am to 3 pm, and 91.1% were exposed to the sun more than one hour per week. Only 48.7% of the mothers gave their children vitamin D supplementation. Conclusion & recommendation: Less than one quarter of the mothers had a good knowledge while about three fifths of the mothers had a positive attitude & less than half of them had a good practice towards vitamin D and its supplementation. Awareness campaigns may help in improving awareness about vitamin D importance.