The nucleation of ε-caprolactam in melts containing water impurities between 3% and 7% w/w was investigated in a batch reactor monitoring melt temperature. The induction times preceding the formation of ε-caprolactam nuclei were inversely proportional to the melt supersaturation and a threshold in the supersaturation of about 6% was found for homogenous nucleation. The interfacial tensions calculated using the classical nucleation theory ranged between 0.8 and 1.5 mJ m - 2 for water content of 3%-7%, respectively. The concomitant increase of the size of the critical nucleus suggested that water inhibits the process of nucleation of ε-caprolactam in melts containing water impurity. This conclusion was further confirmed for the rates of crystal growth of the ε-caprolactam in the melts measured from the rates of temperature increase with time.