OSA uniform color space was used to study the relationship between visual acuity and OSA color contrast. Visual acuity is characterized by 50% minimal separable visual angle using Landolt-C. The OSA color contrast is characterized by the distance between colors in OSA color space. Twenty subjects with normal color vision were tested on 342 test sheers printed with colored Landolt-Cs and background. These results demonstrated that MSVA is approximately inverse log-linearly related to OSA color contrast (R(2) = 80.4%). Although luminance contrast (R(2) = 54.2%) is more salient than chromatic contrast (R(2) = 16.4%), both contrasts can induce very high visual acuity provided that they are sufficiently high. There is also evidence of an additive interaction between chromatic contrast and luminance contrast. Based on these findings, the OSA uniform color space and its color difference formula can be used as a scale for quantifying color contrast to accurately predict the size of colored text or symbols.