Objective：To evaluate the vitamin D status of pregnant women in different seasons from Jiangsu Province. Methods：A total of 18，478 healthy pregnant women were recruited from hospitals located in 8 areas from Jiangsu Province during January 2013 to December 2015，and fast blood samples were collected from all the subjects. Serum 25-hydroxyvitamin D3［25(OH)D3］ and 25-hydroxyvitamin D2［25(OH)D2］ concentrations were measured by liquid chromatography tandem mass spectrometry (LC-MS/MS). The information on characteristics of the pregnant women was collected by questionnaires. The serum concentration of 25-hydroxyvitamin D ［25(OH)D］ was the total concentration of 25(OH)D3 and 25(OH)D2. Results：The average serum concentration of 25(OH)D was (19.2±9.4) ng/mL among all the subjects. The rate of vitamin D deficiency ［25(OH)D＜20ng/mL］ in the subjects was 59.7%，the rate of serious vitamin D deficiency ［25(OH)D＜12ng/mL］ was 24.9%，and the rate of adequacy［25(OH)D＞30ng/mL］ was 13.7%. The average serum concentration of 25(OH)D was (17.3±8.5) ng/mL，(18.2±9.0)ng/mL，and (20.5±9.7)ng/mL in the year of 2013，2014，and 2015，respectively，and similarly the vitamin D deficiency rate was 69.4%，63.6%，and 54.4%，respectively in 2013，2014，and 2015. There were significant differences in the levels of serum 25(OH)D among the subjects in different years (P＜0.01). The average serum concentration of 25(OH)D was (19.2±9.5) ng/mL，(19.6±9.0) ng/mL，and (18.4±8.7) ng/mL in the southern，middle and northern part of Jiangsu Province，respectively，and the corresponding rate of vitamin D deficiency was 60.0%，57.9%，and 62.8%，respectively. There were significant differences in the serum concentrations of 25(OH)D among the subjects from the three regions (P＜0.01). The serum concentrations of 25(OH)D were positively correlated with ages of the subjects (r=0.8，P＜0.01). Seasonal difference was found in the serum concentrations of 25(OH)D. The average serum concentration of 25(OH)D in summer and autumn was higher than that in spring and winter，and the average serum concentration of 25(OH)D was (22.7±9.2) ng/mL，(22.2±9.3) ng/mL，(15.3±7.3) ng/mL，and (12.3±6.4) ng/mL in summer，autumn，spring，winter，respectively. Conclusion：It is vital for obstetrician to monitor the maternal vitamin D levels and guide the pregnant women with vitamin D deficiency to take vitamin D supplements timely.