Effects of heat-set temperature in yarn formation process on the structure and properties of two different polyester fibers, undrawn yarn (UDY) and partially-oriented yarn (POY), were investigated. Drawing temperature was fixed at $80^{circ}C$ for UDY and $90^{circ}C$ for POY which had been determined as the optimum temperature in a previous study. The heat plate temperature was varied by $5^{circ}C$ intervals near the critical crystallization temperature ($T_{cc}$) of polyester in order to determine the effects of the temperature changes on the orientation, crystallization, fiber evenness, mechanical and dyeing properties of the polyester fibers. Results indicated that the heat plate temperature did not have a great effect on the mechanical properties and evenness of the fibers. However, a marginal reduction of dye exhaustion and dyeing rate was caused with increase in heat plate temperature. These effects were discussed with respect to the structural changes of the fibers in the fiber formation process.