As-spun polypropylene (PP) fibres, obtained under a one-step statistical experimental design using orthogonal arrays and involving all the common spinning parameters were studied with wide angle X-ray scattering (WAXS). The WAXS results revealed that the micro-structure of PP fibres can be altered progressively from less-ordered para-crystalline states to highly-ordered crystalline states with an α-monoclinic lattice. The degree of structural order has been evaluated quantitatively in terms of (W ½ ) −1 , the reciprocal of the half-height width of the first WAXS reflection peak. On the basis of such quantitative evaluation, which is shown to be consistent with the conclusions derived from “traditional” qualitative assessment, comprehensive quantitative analysis of the effects of processing parameters and their interactions on the degree of structural order is accomplished, using systematic but simple statistical methods. Parameters significantly affecting structure, including types of raw materials, winding speed, spinning temperature, application speed of spin finish and metering pump speed are identified, and correlation between structure and parameter setting is established in a concise statistical model. The model indicates clearly the combination of parameter levels for increasing or reducing the degree of structural order over the whole range from essentially amorphous to highly crystalline forms. Comparisons with the “conventional” approach of “one factor at a time” demonstrated the validity of the new approach and its significant advantages. The latter includes the economy in experiment scale, efficiency in result analysis and a comprehensive overview of the process being studied, which covers effects arising from synergistic interactions as well as from individual parameters.