The impact of vitamin D status on bone health and other health conditions is receiving increasingly attention. We aimed to determine the association between environmental factors and vitamin D intake by examining serum 25-hydroxy vitamin D [25(OH)D] levels in Thai children. We conducted a cross sectional study among 477 Thai children from 4 regions in Thailand. Vitamin D intake was assessed using a self-administered questionnaire completed by the older children or by the parents for younger children. Dietary vitamin D intake was assessed using a semi-quantitative food frequency questionnaire. A serum 25(OH)D level was examined for each subject using a chemiluminescence immunoassay. We used structural equation modeling (SEM) to assess the association between studied factors and the serum 25(OH)D level. The final model showed a significant association between sunlight exposure and the serum 25(OH)D level (β = 0.65, p < 0.01), but not between dietary vitamin D intake and the serum 25(OH)D level (p = 0.01, p = 0.77), suggesting sunlight exposure is more important for the vitamin D status than dietary vitamin D intake.