This paper reports the use of near infrared (NIR) spectroscopy as a process analytical technology (PAT) tool for monitoring the metformin (N,N--dimethylimidodicarbonimidic diamide) hydrochloride and poly(vinyl pyrrolidone) (PVP) mixing process, which is the first stage in tablet production. Blend homogeneity was tested using the non-invasive NIR spectroscopy method and the partial least squares (PLS) regression model was applied for the analysis of the obtained spectra. Simultaneously, the critical parameter (metformin hydrochloride content) was monitored by a classical analytical technique, the validated HPLC method, commonly used for this purpose. Based on the high sensitivity of the model developed in this study, as well as the established correlation among the results obtained by different methods, it could be concluded that the proposed rapid and non-invasive technique could be an effecttive tool for the monitoring of one of the critical manufacturing steps in the production solid dosage forms.