Experiments were carried out in a spouted bed with auxiliary gas introduced horizontally. Auxiliary gas introduced horizontally has an obvious effect on the minimum spouting gas velocity; the minimum spouting gas velocity decreases with increasing auxiliary gas velocity. An empirical equation for the minimum spouting velocity is modified to fit the experimental data. With an increase in the proportion of the auxiliary gas for a fixed total gas flow, the fountain height decreases, but the relative voidage-in the spout decreases, which means that more particles are circulated. Comparatively, the spouting gas has a distinct effect on the particle velocity in the spouting region, but the auxiliary gas velocity affects the particle velocity in the annular region markedly. The radial profiles of relative voidage and particle velocity at different axial heights are also studied in detail.