Foam-gelcasting-freeze drying method is developed to fabricate porous Y2SiO5 ceramic with ultrahigh porosity of 92.2%-95.8% and isotropous multiple pore structures. As prepared porous samples have quite low shrinkages of 0.8%-1.9% during demolding and drying processes, lightweights of 0.19-0.35g/cm(3), and extremely low thermal conductivities of 0.054-0.089W(mK)(-1). Our approach combines the merits of foam-gelcasting method and freeze drying method. It is a simple and effective method to fabricate porous ceramics with very high porosity and extremely low thermal conductivity through low shrinkage of green body and near net complex shape forming.