Abstract: A method for controlling production process by performing near-infrared absorptiometric analysis by simple procedures in an accurate manner, in which control of production process step can be realized at a high accuracy by simple operation based on the thereby obtained analytical results, the said method comprising taking each absorbance spectrum for a plurality of standard samples in an analysis range including near-infrared region, calculating the average intensity and standard deviations for each of selected wave lengths to construct a data base, taking an absorbance spectrum in the said analysis range for each of analysis samples and comparing it with the data base in order to judge whether or not the intensity of the absorbance spectrum is within an assumed tolerance limit determined based on the stored standard deviations of the standard samples in the data base to thereby obtain control data by comparing, when wave lengths at which the observed intensity is outside the tolerance limit are present, thes