The impurity distribution inside crystalline layers in static layer crystallizations was explored theoretically and experimentally for a binary eutectic mixture of caprolactam and water. The impurity distribution in the layer is modeled by a mass balance equation coupled with an energy balance equation. The mass balance equation is established with a combination of the growth of the layer and the diffusional movement of impurity. The mathematical model was solved by a numerical method. The predictions are discussed with respect to the interfacial distribution coefficient, concentration, and temperature at the solid-liquid interface, crystalline layer thickness, and concentration of the layer. The impurity distribution obtained by the model was appropriately verified with the results obtained by the experiments.