The horizontal stirred bed reactor (HSBR) is a prevalent biomass pyrolysis reactor due to its effective seal, excellent control of temperature and residence time, and capacity to handle a wide range of particle diameters. This paper focused on the effects of various parameters on residence time distribution (RTD) and particle flow behavior in the HSBR. The RTD of biomass particles in a custom-built HSBR was measured using the impulse response method. The effects of operational parameters (including flow rate and agitator rotation rate), material flow properties (characterized by the angle of repose), and design parameters (including the number of blades and blade angle) on solid hold-up, mean residence time (MRT) and relative variance of residence time were investigated. The solid hold-up was affected by the rotation rate, flow rate, blade number, blade angles and material flow properties. The flow rate and material flow properties had a significant influence on the MRT while the effect of the other three parameters on the MRT was minimal. The relative variance was primarily influenced by the flow rate, rotation rate, blade number and material flow properties. The effect of the flow properties on the relative variance was irregular. The inter-particle mixing mainly resulted from agitator stirring. Hence, the inter-particle mixing was enhanced with the increase of the rotation rate and blade number. As such, it is essential to further examine the effect of material flow properties on inter-particle mixing using a modeling approach. (C) 2014 Elsevier B.V. All rights reserved.