The effect of drawing and heat treatment of PET filament on the various mechanical properties were studied. The effect of draw ratio, heat treatment condition and measuring condition upon tensile characteristics and dynamic properties were examined in terms of structural factors such as crystallinity, orientation and molecular structure. Relation between yield stress and extension speed presents a considerable dispersion depending upon the measuring temperatures. However, high drafted and heat treated samples were given superposition of the individual curve by moving it horizontally along with the axis of extension. Consequently, relation between logarithm of aT, a horizontal moving factor, and 1/T is not linear, however, reasonable value can be obtained when calculated the value for apparent activation energy. Deflection point of the mechanical properties were shown in the range of 2.0 to 2.5 drawing ratio, where it can be determined the existence of changing range of the fiber structure.