The present work reports studies on the mixing and combustion characteristics of cotton stalk (CS) with 10-100 mm in length in a fluidized bed. Effects of length and initial weight percentage of CS, diameter of alumina bed material as well as gas velocity on the mixing characteristics of CS with alumina were investigated. CS can mix well with 0.6-1 mm alumina at fluidization number N = 3-8. Fluidized bed combustion of pure CS was conducted in a 0.2 MWth test facility. The concentrations of major gaseous pollutants (CO, SO2 and NO) in flue (stack) gas were measured. The combustion efficiency of CS is over 99.5%. Additionally, the experiments researched the agglomeration characteristics of bed materials: silica sand and alumina. SEM/EDX analyses on silica samples suggest that the high alkali metals content may cause the formation of the coating around silica particles. The coating consists of compounds with low melting temperature and can result in the bed agglomeration. By contrast, alumina is difficult to react with alkali metals from CS ash after 38 h combustion. (C) 2008 Elsevier Ltd. All rights reserved.