Pearl-scale goldfish（Carassius auratus） is a rare goldfish variety. To demonstrate the mechanism of its mutation, the microstructures of the scale of Crown Pearl-scale goldfish and Ranchu goldfish were studied by H.E and special staining methods. The results showed that: a) the middle of Crown Pearl-scale goldfish scale was more thickened than of Ranchu Goldfish; b) the collagenous fiber in the scales of Crown Pearl-scale Goldfish were looser and more disorganized than in Ranchu Goldfish, c) the fiber layer of Crown Pearl-scale goldfish scale was full of loose connective tissue matrix and cells, which was a first discovery in scales of the Osteichthyes. The mutation of Pearl-scale goldfish scale is mostly due to the change of fiber layer in the scale.