Structural changes of polyester yam with false-twist draw texturing parameters have been studied using a high-temperature heater, high texturing speeds, short residence time in the heater and a short yarn path. The dependence of three structural parameters, viz. crystalline orientation, crystal size and birefringence, on texturing temperature, yam residence time in the heater and draw ratio has also been studied. At high texturing speeds, the crystalline orientation and crystal size decrease due to low thermal input. Crystalline orientation tends to increase at high texturing temperatures and draw ratios.