The recession behavior of Lu2SiO5 and Lu2Si2O7 under high speed steam jet with a velocity of 50 m/s in temperature range between 1300o and 1500oC was compared. Material recession and porous microstructure were observed on the bulk surface for all samples after steam jet tests at the elevated temperatures. The porous structure for Lu2Si2O7 bulk samples become refine with increasing test temperature. On the other hand, the porosity of the porous structure for Lu2SiO5 bulk samples reduced with increasing test temperatures. Phase change was observed for the test of Lu2Si2O7 sample. Lu2SiO5 phase was formed on the Lu2Si2O7 bulk surface in the 1400oC test and Lu2Si2O7 phase was formed again on the surface of the bulk in the test at 1500oC. No phase change was observed in the tests for Lu2SiO5 between 1300o and 1500oC.