Objective To explore the association between 25-hydroxyvitamin D (25OHD) level and risk of the onset of metabolic syndrome (MS) in people in Chengdu. Methods In total, 474 participants were selected randomly by cluster sampling from one urban district and two rural villages in Longquanyi district of Chengdu. The data of sociodemographic information, lifestyle and family history were collected by questionnaires. Binary logistic regression was performed to assess the relationship between baseline 25OHD level and incident of MS, while multiple linear regression was conducted to analyze the relationship between baseline 25OHD level and insulin resistance. Results Four hundred seventy-four people were enrolled in the cohort study, 39 of them developed MS, with the incidences of 20.8 events per 1 000 person years. Among women, low 25OHD status was significantly associated with the risk of developing MS (OR=4.29, 95%CI 1.05 to 29.50, P=0.044) after adjustment for multiple potential confounders. In a multiple linear regression analysis, low 25OHD level of baseline was independently associated with the increased HOMA-IR over a 4-year period among Chengdu individuals (P<0.05) and was independently related to the decreased ISIcomp over a 4-year period in female (P<0.05). Conclusions The current prospective study suggests that low 25OHD level may contribute to increase insulin resistance in Chengdu population. Furthermore, low 25OHD level may increase the risk of MS among women in Chengdu.