Polyoxymethylene (polytrioxane) with wry high degree of erystallinity cain be obtained by γ-irradiation of trioxane single crystals with Co60 source．In the rotation diagram of polytrioxane obtained by γ-irradiation of trioxane there appear some new diffraction spots in addition to that for ordinary polyoxymethylene．Polytrioxane can be splitted into fibers along the C-axis of the original trioxane crystal．The new diffraction spots showing on the rotation diagram would gradually disappear by heat treatment of the sample．By comparing the spaces occupied by polytrioxane and trioxane molecules，we consider that there are four kinds of crystalline zones with different orientation in the polytrioxane crystals，which join together forming many crankshaft-shaped crys-tallites.