Objective： To investigate the variation of visual acuity （VA） at different contrast levels under bright and dark backgrounds in healthy adults. Methods： Fifty-four men （ 108 eyes） with normal VA were enrolled in this study. LogMAR VA was measured at 4 contrast levels （100 %, 25 %, 10%, and 5 % ） under bright and dark backgrounds with multi-functional visual acuity tester （MFVA-100）. The relationship of VA between bright and dark backgrounds was analyzed. Results： （1） Subjects with lower contrast level had significantly worse VA than those with higher contrast level when the background was identical （P〈0. 001）; VA decreased gradually with the decrease of contrast level. At the same contrast level, the VA under dark background group was significantly worse than that under bright background group （P〈0. 001）. （2） The VA at contrast level 100% under bright background was not linearly related to those under dark background （P〉0.05）, but was linearly related to those at other contrast levels under bright background （P〈0. 001）. Under dark background, the VA at contrast level 100% was linearly related to those at other contrast levels（P〈0. 001）. （3） The fluctuating differences （log unit） of VA increased with the decrease of contrast level, with the maximal difference found at contrast level 5 ; under dark background. Conclusion： The VA of healthy men under bright background is better than that under dark background. The VA decreases and individual variation increases gradually with the decrease of contrast level. There is no linear correlation of VA between the bright and dark backgrounds.