Y203 -doped aluminum nitride(AIN) ceramic with thermal conductivity varying from 90 W/m K-162.5W/mo K at room temperature were produced by powder injection molding (PIM). The effects of the amount of additives and sintering condition on the composition of second phase. and the thermal properties are studied and discussed in detail. The experimental results show that the composition, distribution and oxygen content of the second phase have a great effect on the thermal conductivity.