Si2N2O powders were synthesized at low temperatures by a Y2O3-assisted-carbothermal reduction nitridation (CRN) with mesoporous silica/carbon composite as raw material. Experimental results showed that with the addition of Y2O3, the CRN reaction temperature decreased from 1380°C to 1250°C. The mechanism for Y2O3 reducing the CRN temperature was discussed in detail. It was found that the occurrence of Si2N2O at low temperatures was due to the formation of an eutectic intermediate phase as Y2SiO5, which was the reaction product of Y2O3 and mesoporous SiO2. In addition, spherical and rod-like Si2N2O powders were found to be readily obtained by selecting the mesoporous silica/carbon composite precursors with mesoporous silica spheres and rod-like SBA-15, respectively.