The fine structure of PPTA mat-like crystal has been studied by solvent etching technique and electron microscopy．It has been found that the mat-like crystal is made of zigzag fibrillar structure oriented along the shear direction in the film．The periodical length of the zigzag fibrils is about one micron，corresponding to the width of a band in mat-like crystal．Therefore．the morphology of mat-like crystal observed by polarizing microscopy is an optical effect resulted from the periodical structure of the zigzag fibrils．The structure of an isolated fibril has also been observed． It is made of consecutively linked plates which may be formed from the moleeular slipping within the domain structure during the shear process．A new model is suggested to explain the structure of the PPTA film with mat-like crystalline morphology．