Vitamin D deficiency is an unrecognized health problem worldwide. This investigation was carried out to assess the level of vitamin D and to figure out the reasons of vitamin D insufficiency in children living in Jeddah city, Kingdom of Saudi Arabia. This investigation was carried out in Pediatric and Maternity Hospital Almosadia in Jeddah, Saudi Arabia from October till December, 2015. One hundred healthy children were involved in this study, aged 5 to 15 year-old. Serum calcium and 25-hydroxyvitamin D levels were estimated. Supplemental vitamin D consumption and sun-exposure time were determined. Respondents age was between 1 to 15 year-old. The males were 45(45%) and females were 55 (55%). 98 % of them were Saudis, 1% were Yemeni and 1% were Palestinian. The average exposure to sun light was 7.12±4.39 minutes/day. The mean of daily vitamin D intake was 163.8±55.44 units/day and 26% of children were taking more than 200 IU/day. The average of vitamin D serum level was 15.01±4.5 ng/ml and only 16% of subjects had serum concentration of vitamin D >20 ng/ml (P=0.036). The calcium serum mean level was 7.24±2.04 mg/dl (P=.001). Eminent prevalence of vitamin D insufficiency was observed among very healthful children residing in a sunny Jeddah city. Proper exposure to sunlight and vitamin D supplements can prevent vitamin D deficiency.