Spout deflection is a typical instability phenomenon in spout fluidized beds and can greatly affect the homogeneity of the gas-solid system as well as product quality. However, few studies have been conducted to quantify the relation between the spout deflection and particle density. In this paper, the effects of particle density on the spout deflection under three scenarios are investigated, including constant fluidization velocity, scaled-up fluidization velocity and time-dependent particle density. The spout deflection angle is used to quantify spout deflecting movement. The results show that non-alternating spout deflection happens if particle density is less than 2130 kg/m(3) at a constant fluidization velocity. The amplitude, deflection speed and regularity of alternating spout deflection keep unchanged if particle density ranges from 2230 kg/m(3) to 3830 kg/m(3) at a constant fluidization velocity. Then, when particle density ranges from 1830 kg/m(3) to 3830 kg/m(3) and meanwhile fluidization velocity are scaled up, alternating spout deflection also happens, where the main characteristics of alternating spout deflection, including amplitude, deflection speed and regularity, however, keep constant even if particle density varies. In addition, if particle density is changed with time, the amplitude, deflection speed and regularity of the alternating spout deflection will also keep constant, indicating that the hydrodynamics of the alternating spout deflection has little relationship with initial particle position state and particle density. This study confirms the effects of particle density on the spout deflection behavior in the spout fluidized bed. (C) 2020 Elsevier B.V. All rights reserved.