The objective of this study was to investigate the flow structures and mixing mechanisms of a gas-solid two-phase jet from a burner employed in the utility boiler. Laboratory experiments were conducted in a 0.15 m internal diameter test facility. Gas-solid jet flow downstream of the burner exit was measured by a fiber optic probe. Local solid concentration and particle size distribution were obtained using the probe that was traversed over the cross-section of the jet. The effects of the side flow on the primary air gas-solid flow characteristics were also studied. The measurements showed the availability of fiber optic probe to investigate the gas-solid jet flow downstream the industrial burner nozzle with high solid concentration. Obvious slip between the gas phase and the solid phase in the gas-solid jet flow was found in the experiments. The side flow disturbed the solid concentration distribution in the jet, a more smooth solid concentration profile across the jet can be achieved after the side flow was introduced. The particle size distributions in the jet were similar with the distributions of the solid concentration, the particles with large diameters always appeared in the zones where the solid concentrations were high. (c) 2005 Elsevier Ltd. All rights reserved.