Abstract: The studied specimen of freshwater cultured non- nucleated pearls are taken from Ezhou City,Hubei Province,which is one of the important pearl- cultured bases in China. Studied by microscope on the shape,surface flaw,section and“Leyao”——a ditch- like charac- ter on the surface of pearl,the“Leyao”is regular straight line- like,parallel to each other and usually found on surface of the pearls with diameter more than 4mm and oval shape resulted from rotated growth,accompanied by nail- like lines with same direction.It can be observed under SEM that the aragonite layers become thinner and cracked,and curve down from the normal to the“Leyao” part. The“Leyao” is a U-like ditch on the section and the aragonite layers are continued on the wall of ditch if a intervallic lack of aragonite layers.The“Leyao”is a precipitous wall and aragonite layers are in disorder on the wall if aragonite layers are lack com- pletely.The“Leyao”is possibly related to the lack of secrete ability of pearl sac partially and pearl- rotated growth relatively to pearl sac.