In this study, the effects of two types of SiO2 sources (amorphous micro-sized SiO2 particles and in situ oxidised SiC nanopowder) on the thermal shock resistance of porous Al2O3 mullite ceramics were compared. The thermal shock resistance was evaluated by measuring the elastic modulus determined by the non-destructive impulse excitation technique after each thermal shock cycle. It was found that materials modified by addition of 2.5 and 5.0 wt% of SiC nanopowder (equivalent to 3.7 and 7.3 wt% of SiO2) have an improved thermal shock resistance compared to unmodified corundum ceramics and ceramics modified with amorphous micro-sized SiO2.