Objective To investigate the refractive error and best corrective visual acuity of preschoolers aged 3 to 6 years. Methods Ten kindergartens were randomly selected from different districts in the Guangzhou area. Refractive error and best corrected visual acuity of the preschoolers were measured. Refractive error was determined by an autorefractor, which was rechecked by cycloplegic retinoscopy with cyclopentolate. Best corrected visual acuity was measured with an EDTRS vision chart. Data was analyzed with one-way ANOVA using Bonferroni correction. Results Two thousand four hundred and eighty children were examined in the study. There were 201 boys and 172 girls in the 3-year-old group and 434/384, 437/410, 238/204 in the 4-, 5- and 6-year-old groups, respectively. The mean ages in months were 43.3±2.8, 53.8±3.3, 65.5±3.4 and 75.1 ±2.6, respectively. The spherical equivalent refractions of the corresponding age groups were (1.66±0.70)D, (1.67±0.80)D, (1.59±0.81)D and (1.48±0.72)D, respectively. And the differences among the groups were statistically significant (P=0.000). The Bonferroni multiple comparisons showed that the difference between any pair of groups was statistically significant, except for that between the 3-year-old and 4-year-old groups, and between the 3-year-old and 5-year-old groups. The best corrected visual acuities on the LogMAR scale for the corresponding age groups were 0.26±0.14, 0.18±0.10, 0.13± 0.08 and 0.10±0.08, respectively. The difference among groups was statistically significant (P=0.000). The Bonferroni multiple comparisons between any pair of groups were also statistically significant (P=0.000). Conclusion Hyperopic refractive error gradually decreases with an increase of age during the 3rd to 6th years. The norms of the best corrected visual acuity shows a slow rise during this period, which indicates that age is an indispensable factor in making a diagnosis of amblyopia in children.