In order to purify diethylene glycol as main impurity included in p-dioxanone, SLE (solid-liquid equilibria) and mixture density on two components system of p-dioxanone and diethylene glycol were measured and a layered melt crystallization with seed has been applied. The SLE of p-dioxanone and diethylene glycol were a simple eutectic system and the temperature and PDX concentration at eutectic point were 0.08 and 246 K, respectively. Densities of their binary mixtures were well fitted by the best correlation equation, ρl=0.405+1.361x+0.002T.0.004xT. In the melt crystallization, the growth rate (G) was proportional to the 1.5th power of the subcooling degree. The effective distribution coefficient (Keff) as the degree of impurity removal was observed to increase with increasing the growth rate and initial p-dioxanone concentration. And also, Keff was correlated with Z function using Wintermantel’s model such as Keef = .0.0604+6.392×Z. Finally, PDX purity through the optimization of this process can be obtained over 99％.