Impurities obtained in c-caprolactam depend either on the raw material used to obtain cyclohexanone (cyclohexane, phenol, or cyclohexanol) or on the procedure. The usual impurities are cyclohexanone oxime (CHN-ox), aniline, o-toluidine, octahydrophenazine, phenol, epsilon-caprolactone, cyclohexylamine, etc. Moreover, methyl-delta-valerolactams (Me-VLMs) are the typical impurities obtained in the epsilon-caprolactam production when the latter is prepared from oximation and further Beckmann rearrangement of a cyclohexanone, previously obtained from cyclohexanol dehydrogenation. On the other hand, the effect of these impurities on the PZ parameter, characteristic of the quality of epsilon-caprolactam, has been experimentally determined. The value of the PZ parameter gives an idea of the amount and strength of the oxidizable impurities on epsilon-caprolactam. To assess the effect of the impurities, these were added in different concentrations to a commercial epsilon-caprolactam. It was found that traces of aniline, o-toluidine CHN-ox, phenol, and octahydrophenazine caused a significant reduction in the PZ number while the effect of Me-VLM and cyclohexylamine was less important.