In the previous paper1), the relationship between necking characteristic factors and neck angle which is a parameter expressing the characteristics of the necking geometry were discussed for undrawn polyester fibers.The present paper intends to investigate the drawing mechanism of polyester fibers on the basis of the informations obtained in the previous paper.1) The results obtained in the most ideal drawing system equipped with the hot-pin leads us to conclude that substantial conditions for occuring necking are hot-pin temperature and feed roll speed. The necking angle is affected decidedly by these factors, and the necking properties such as. draw ratio and necking tension, are determined only by the necking angle.The necking draw ratio is not equal to the machine draw ratio defined as the speed ratio of two rollers. The relationship between the necking draw ratio and the machine draw ratio may be expressed by following equation:Machine DR=Necking DR+2nd draw2) The neck angle estimated from the model undrauring using WLF equation agrees well the experimental results.3) The experimental relationship between the necking drawing and 2nd drawing is discussed for the model and industrial drawings.4) The neck angle is closely related to the aging condition of the undrawn polyester fibers.The increase of aging time enlarges the neck angle and the local variation.