PURPOSE: To improve mechanical strength, thermal expansion coefficient and dimensional stability by adjusting density, degree of crystalline orientation and heat shrinking stress of a polyoxymethylene biaxially drawn sheet or film in a specific range.

CONSTITUTION: A sheet or a film characterized by that it is composed of a polyoxymethylene whose main constituting unit is oxymethylene group-(CH2O)- and that the degree of crystallinity measured by means of density measurement is in the range of 55W75%, the both degrees of crystallinity measured from end and edge in two directions by means of X-ray diffractometry are in the range of 70W95%, and the heat shrinking stress at 130°C is in the range of 5W100kg/cm2, has excellent mechanical properties such as tensile strength, tensile modulus and so on, and a low thermal expansion coefficient whose value in the range of 0W60°C is -10×10-6W10×10-6 cm/cm/°C. It is more preferrable that the degree of crystallinity is 60W75%, the degree of crystalline orientation is 75W95% and the heat shrinking stress (130°C) is 15W100kg/cm2. In this case, it is possible to obtain a sheet or a film having more balanced characteristics.