A method by measuring the slip resistance between particles was used to determine the agglomeration tendency in fluidized bed combustion of biomass. Solid particles were taken from different stages of biomass combustion in a fluidized bed and loaded into a bench-scale test apparatus with two concentric cylinders. A precision variable frequency motor and a torque sensor were employed to measure the torque driven by the inner cylinder at a constant speed, which is directly related to the slip resistance of the solid particles. The measurement results showed significant difference in the slip resistance of the bed solids taken from different stages of biomass combustion at different operating temperatures. A strong correlation was found between the onset of agglomeration and increase in the slip resistance, especially near the onset of agglomeration, due to the build-up of molten biomass ashes, presence of liquid bridges between particles and formation of incipient agglomerates. With further validation, the method developed in the present study can potentially be used to quantify agglomeration tendency in a fluidized bed reactor and characterize the dynamic process of agglomeration. (C) 2014 Elsevier Ltd. All rights reserved.