This study was to investigate the concentration of cord serum 25-hydroxyvitamin D (25OHD) in a birth cohort in Guangzhou, China and determine whether maternal lifestyle factors had any effect on these levels. The prevalence of vitamin D deficiency was higher in infants born in winter months, compared to those born in summer. However, abundant sunshine and a summer birth could not protect infants from being born with vitamin D deficiency. Meanwhile, vitamin D supplementation during pregnancy was effective in raising cord serum vitamin D levels.