Silicon nitride (Si₃N₄) which possess excellent mechanical properties, chemical properties and physical properties have been widely used in chemical industry, metallurgy, aerospace and other fields. Y₂O₃ nanoparticle (NP) catalysts were homogeneously deposited on the surface of Si powders by an in-situ precipitation method using PEG as surfactant and NH₃.H₂O as precipitant. The effects of various processing parameters including the amount of catalyst and nitridation temperature on the synthesis of Si₃N₄ were investigated. Phase composition and microstructure of the Si₃N₄ were characterized by X-ray diffraction, field emission-scanning electron microscopy equipped with EDS. The results showed that: 1) For the sample nitrided at 1350 ℃ for 2 h with 1 wt% of Y₂O₃ NPs as catalysts, residual silicon in the final sample was less than 1 wt%; 2) Lots of Si₃N₄ whiskers with 20~200 nm in diameter and several microns in length was formed in the final products. Vapor-Vapor-Solid (VVS) growth mechanism might be responsible for the growth of Si₃N₄ whiskers.