PURPOSE: To systematically examine the association between ocular biometry and retinal vascular caliber in Singapore Chinese preschoolers aged 48 to 72 months. METHODS: A total of 469 Singapore Chinese children aged 48 to 72 months were recruited through the Strabismus, Amblyopia and Refractive Error Study in Singaporean Chinese Preschoolers (STARS) from 2006 to 2008. According to standardized protocols, cycloplegic autorefraction, ocular biometry measurements, and retinal photography were performed. Retinal vascular caliber was measured quantitatively and was summarized as the central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE), respectively. Ocular magnification was corrected by using the Bengtsson formula. RESULTS: The mean retinal arteriolar and venular calibers were 156.08 μm and 219.55 μm in boys, and 161.96 μm and 224.25 μm in girls, respectively. In multiple linear regression adjusted for age, sex, father's education, parental myopia history, mean arterial blood pressure, body mass index, and spherical equivalent, each 1.0 mm increase in axial length was associated with a 3.52 μm decrease in retinal arteriolar caliber (P = 0.023) and a 5.55 μm decrease in retinal venular caliber (P = 0.008). Each 1.00 mm increase in corneal curvature was associated with a 13.79 μm decrease (P = 0.004) in retinal venular caliber. CONCLUSIONS: In very young children aged 48 to 72 months, narrower retinal arteriolar and venular caliber was associated with elongated axial length. Narrower retinal venular caliber was associated with larger corneal curvature. This suggests that the major structural correlate of myopia might have an effect on retinal microvasculature from early childhood.