Perhydropolysilazane, a preceramic polymer for silicon nitride ceramics, was synthesized by the ammonolysis of dichlorosilane and characterized by FT-IR, GPC, TG, XRD and elemental analysis. The main backbone of the as-synthesized precursor oligomer was［SiH₂NH］_n, with a number average molecular weight of 106 and a weight average molecular weight of 178. The cured precursor polymer was converted into brown ceramic powder after pyrolysis at 1000℃ in nitrogen atmosphere, and the ceramic yield was 78wt%. X-ray patterns showed that the main phases of the polymer-derived ceramic product at 1400℃ in nitrogen atmosphere were α-Si₃N₄ and some free silicon, and the empirical chemical formula for the product was SiN_1.036O_0.060C_0.028 by elemental analysis. After further treatment at 1600℃ in nitrogen atmosphere, extremely weak diffraction peaks for free silicon and intense peaks for α-Si₃N₄ were observed by XRD patterns, however, there was no phase transition from α-Si₃N₄to β-Si₃N₄all along.