Objective: To understand the serum vitamin D and vitamin K 1 levels of children in the Qingdao area, so as to provide scientific grounds for appropriate vitamin supplementation. Methods: A total of 4 469 children aged 0-14 years old, who attended the children s healthcare outpatient clinics of a tertiary hospital in Qingdao, were enrolled in the current study between January 2023 and July 2024. The levels of vitamin D and vitamin K 1 were measured by liquid chromatography tandem mass spectrometry. The inter group differences were analyzed using Chi square test, Wilcoxon rank sum test, and Kruskal-Wallis H test. The correlation analysis of vitamin D and vitamin K 1 levels with age was performed using the Spearman correlation. Results: The serum vitamin D level among children was 28.72(22.67, 36.26)ng/mL. The vitamin D deficiency and insufficiency rates were 2.10% and 14.59 %, respectively. The serum 25-(OH)D 2 level was 0.29(0.14, 0.53)ng/mL, the serum 25-(OH)D 3 level was 27.99( 21.78 , 35.57)ng/mL and the serum vitamin K 1 level was 0.54(0.29, 1.04)ng/mL. The vitamin K 1 deficiency rate was 13.76%. Among different age stages, the serum vitamin D level was highest in infancy [37.45(30.39, 43.87)ng/mL] and lowest in school age children [22.39(18.00, 26.97)ng/mL]; the level of vitamin K 1 was highest in preschool children [0.79(0.41, 1.51) ng/mL] and lowest in school age children[0.45 (0.26, 0.76) ng/mL]; the serum vitamin D deficiency and insufficiency rates were highest in school age children (5.03% and 30.81%); the vitamin K 1 deficiency rate was highest in infancy (21.53%) ( H/χ 2=1 698.31, 253.70 , 137.85 , 583.79, 89.30, all P <0.05). Among different seasons, the serum vitamin D and vitamin K 1 levels were lowest in the winter [26.74(18.37, 35.86) and 0.50 (0.27, 0.94)ng/mL; H =50.71, 7.86]; the vitamin D deficiency and insufficiency rates were highest in the winter (5.41% and 24.80%; χ 2=59.93, 83.35) (all P <0.05). The serum vitamin D level had a moderate negative correlation with age ( r =-0.62), and there was a low positive correlation between the serum vitamin D and vitamin K 1 levels in infancy and early childhood ( r =0.21, 0.26) (all P <0.05). Conclusions The serum vitamin D and vitamin K 1 levels are lowest in school age children and in the winter, and the serum vitamin K 1 deficiency rate is highest in infancy. There is a need to focus on critical periods of infancy and school age, and strengthen interventions during the high risk winter season. The nutritional status of vitamin D and vitamin K 1 in children should be enhanced.