Abstract: Devitrification was observed in the central portion of the nanoscale porous silica glasses which were sunk in Nd³⁺-ZBLAN melt for filling in it's surface layer with Nd ³⁺-ZBLAN.The devitrified area has crystallization slices in the size of 50-100μm with nanoscale pores and channels remain in the fish scale-like appearance.The com posite layers remain amorphous.Silica etching by sodium hydroxide in the pores is considered to initiate the seeds of crystallization and the high pressure in the pores may facilitate the development of crystallization.