Fiber structure development in the poly(ethylene terephthalate) fiber drawing process was investigated by on-line measurement of wide-angle and small-angle x-ray scattering employing both a high-luminance x-ray source and a carbon dioxide laser-heated-drawing system. Intensity profile of transmitted x-ray confirmed the location of the neck-drawing point. Obtained diffraction images had a time-resolution of several milliseconds, which still leaves a great capacity for improvement. Crystal diffraction appeared in the wide-angle x-ray images almost instantaneously about 20 ms after necking, whereas a four-point SAXS pattern appeared immediately after necking. With the elapse of time after necking, the four-point scattering pattern changed to a meridional two-point shape.