Abstract: Alpha-silicon nitride whiskers were prepared by the"in-situ" growth of ultrafine amorphous silicon nitride powders.The experiment was carried out at 1400~1450℃ for 1~4 hours.When the experiment was conducted in the atmosphere of nitrogen with high purity,the nitrogen content,oxygen content and chlorine content in alpha-silicon nitride whiskers obtained were 32%-34%,8%~6% and~0.1%,respectively.A lot of defects were detected in the whisker.However,when the experiment was completed in an atmosphere of ammonia, the content of nitrogen,oxygen and chlorine in the whiskers changed to 39%,1% and 0.01%,respectively,where nearly "defect-free" in the whisker was detected.