Two-micrometer avenge sized fine silicon-powder, mixed with 300-mu m average sized alumina particles as an inert fluidization conditioner. was nitrided with 90% N-2/10% H-2 mixture gas in a fluidized-bed reactor, operated at temperatures ranging from 1200 to 1300 degrees C. Both batch and semi-continuous nitridation runs were made by feeding solid mixtures of different silicon powder fractions up to 30% by mass. When the content of silicon powder was lower than 5% in the batch operation, no beta-phase was found in the product silicon nitride at any temperature investigated. When mixtures containing 30% or less silicon powder were used for the semi-continuous operation, a-silicon nitride was produced at any temperatures below 1250 degrees C, while feeding mixtures containing 20% silicon powder at 1300 degrees C resulted in the formation of 21% beta-silicon nitride. Increasing silicon powder contents in the feed mixture Facilitated the formation of p-silicon nitride due to the self-agglomeration of powder, which also led to the failure of fluidization.