Polypedates leucomystax are medium in size and slender. The back (dorsal) smooth skin, without folds, bumps or nodules. The color is changing, light yellowish brown, grayish to pale whitish, large and small dark spots, or longitudinal stripes. There is a dark black line or band between the nose and the eye, back past the upper side of the tympanum (ear drum) to the shoulder. The black band is bordered by a thin golden yellow line above it, especially from the eye to the shoulder above the tympanum. A similar golden line is also found on the narrow lip on the sides of the hand, from the elbow to the lateral (side) of the fingers; and on the side of the sole of the foot to the lateral side of the toes. The underside (ventral) is smooth, white to slightly golden in color. The eyes are large and prominent with golden yellow irises, and the color of the upper lip is golden and the lower lip is blackish.
Hands and thighs with black oblique stripes. Fingers on webbed hands are half or almost non-existent. The swimming membranes on the feet are black, reaching the tip of the toes; except on the fourth finger (the longest), only reaching the second segment from the tip.