To find out the optimum heating profile for the nitridation of compacts of graded silicon grains (max 53$mu extrm{m}$) two batches with the addition of MgO and $Mg(NO_3)_3$$cdot$$6H_2O$ to silicon particles were isostatically pressed into compacts. They were nitrided under some different nitriding schedules. The properties such as bulk densitis microstructures and formed phases were measured and observed. The following results were obtained ; 1) About 10% unreacted silicon remained in specimen which was nitrided at 1, 350$^{circ}C$ for 240hrs. 2) One of the step-heating processes 1, 150$^{circ}C$</TEX>-1, 390$^{circ}C$ for 65hrs are then $1, 390^{circ}C$for 50hrs was the low temperature but with that at high temperature. 3) High pressure(10.5kgf/$cm^2$) of nitrogen at 1, 390$^{circ}C$</TEX> accelerated the $alpha$<TEX>$ ightarrow$</TEX>$eta$ transformation of silicon nitride. 4) Magnesium nitrate was superior to magnesium oxide in the role of nitriding aid and the formation of uniform microstructures.