Objective To explore the relationship between 25-hydroxy vitamin D [25(OH)D] and metabolic syndrome (MS) in non-dialysis patients with stage 3–5 chronic kidney disease (CKD). Methods Between January 2014 and May 2015, a total of 61 non-dialysis patients with stage 3–5 CKD were included. The patients’ height, weight, blood lipid, levels of 25(OH)D and serum creatinine were conducted. The relationship between 25(OH)D and MS was analyzed. Results The average level of 25(OH)D was (39.99±17.66) nmol/L. Normal level (≥75 mmol/L) of 25(OH)D was observed in 3.3% (2/61) of the patients, insufficiency of 25(OH)D (≥37.5 nmol/L and <75 nmol/L) was observed in 50.8% (31/61), and deficiency (<37.5 nmol/L) was observed in 45.9% (28/61). The prevalence of MS was 67.2% ( 41/61). The body mass index (BMI), proportion of hypertension, proportion of diabetes mellitus, level of triglyceride in the MS group were higher than those in the non-MS group, while the levels of high-density lipoprotein and 25(OH)D were lower in the MS group than those in the non-MS group, and the differences were statistically significant (P<0.05). The patients’ BMI, proportion of hypertension, level of triglyceride and proportion of MS in the 25(OH)D deficiency group were higher than those in the 25(OH)D non-deficiency group, meanwhile, the level of high-density lopoprotein was lower in the 25(OH)D deficiency group than that in the 25(OH)D non-deficiency group, and the differences were statistically significant (P<0.05). Serum 25(OH)D level was correlated negatively with BMI (r=–0.35, P=0.006) and the level of triglyceride (r=–0.16, P=0.039), and correlated positively with the level of high-density lipoprotein (r=0.18, P=0.026). Conclusions Low level of 25(OH)D and MS are both of high incidence rate in non-dialysis patients with stage 3–5 CKD. 25(OH)D is associated with MS.