Purpose: To study subfoveal choroidal thickness (SFCT) in adult Chinese subjects and its correlation with ocular biometric parameters, refractive error, and age. Design: Population-based longitudinal study. Participants: The population-based Beijing Eye Study 2011 included 3468 individuals with a mean age of 64.6 +/- 9.8 years (range, 50-93 years). Methods: A detailed ophthalmic examination was performed, including spectral-domain optical coherence tomography (SD-OCT) with enhanced depth imaging for measurement of SFCT. Main Outcome Measures: Subfoveal choroidal thickness. Results: The SFCT measurements were available for 3233 subjects (93.2%). Mean SFCT was 253.8 +/- 107.4 mu m (range, 8-854 mu m). In multivariate analysis, SFCT increased with younger age (P<0.001; correlation coefficient r = 4.12; beta coefficient = -0.37), shorter axial length (P<0.001; r = 44.7; beta coefficient = 0.46), male gender (P<0.001; r = 28.5; beta coefficient = -0.13), deeper anterior chamber depth (P<0.001; r = 39.3; beta coefficient = 0.13), thicker lens (P<0.001; r = 26.8; beta coefficient = 0.08), flatter cornea (P<0.001; r = 46.0; beta coefficient = 0.11), and better best-corrected visual acuity (BCVA) (logarithm of minimal angle of resolution; P = 0.001; r = 48.4; beta coefficient = 0.06). In multivariate analysis, SFCT was not significantly associated with blood pressure, ocular perfusion pressure, intraocular pressure, cigarette smoking, alcohol consumption, serum concentrations of lipids and glucose, diabetes mellitus, and arterial hypertension. In the myopic refractive error range of more than -1 diopter (D), SFCT decreased by 15 mu m (95% confidence interval [CI], 11.9-18.5) for every increase in myopic refractive error of 1 D, or by 32 mu m (95% CI, 37.1-26.0) for every increase in axial length of 1 mm. For each year increase in age, the SFCT decreased by 4.1 mu m (95% CI, 4.6-3.7) (multivariate analysis). Conclusions: Subfoveal choroidal thickness with a mean of 254 +/- 107 mu m in elderly subjects with a mean age of 65 years decreased with age (4 mu m per year of age) and myopia (15 mu m per diopter [D] of myopia). It was also associated with male gender and the ocular biometric parameters of a deeper anterior chamber and thicker lens. The association between SFCT and BCVA indicates a functional aspect of SFCT.