This study both measured and compared the mesopic contrast sensitivity function and the visual acuity in both normal and amblyopic eyes from amblyopic children using an ACV (visual acuity analyzer). Twenty one amblyopic children (mean age, 8.48 years; S.D., 1.68 years), 11 strabismic amblyopes and 10 anisometropic amblyopes, were tested. Based on a display of the standard optotypes, the minimal contrast level, at which the optotypes were correctly read for all sizes of displays from a distance of 1m, was measured. The contrast ranged from 1% to 99% and the spatial frequencies ranged from 0.6 to- 30cpd using a Landolt ring composed of low (0.6-2.9 c.p.d.), intermediate (3.0 - 12.9 c.p.d.) and high level (13.0-30.0 c.p.d.) frequencies. As the visual acuity decreased, the mesopic contrast sensitivity function decreased along the contrast sensitivity axis. However, the peak sensitivity was noted at the same spatial frequencies. A comparison between the normal eye and the corresponding amblyopic eye showed that under mesopic conditions, the contrast sensitivity functions decreased more in the intermediate spatial frequencies than in the other spatial frequencies. The mesopic contrast sensitivity function decreased in the amblyopic eyes, which suggests the possibility of its use an adjunct to an evaluation of amblyopia.