A 60-meter-high transparent circulating fluidized bed (CFB) cold experimental apparatus was constructed to experimentally study the axial/radial voidage distribution, and the axial/radial particle diameter distribution in the upper riser. The experiments indicated that the variation of the average voidage in the upper riser with superficial gas velocity could be divided into four successive stages. A modified correlation was proposed to predict the voidage in the upper riser more accurately. For the current 60 m riser, there existed an optimal static bed height of 500 mm which enabled the gas to exactly reach its saturation carrying capacity Gs* of 6.0 kg/(m(2)s). The radial voidage distribution, which was verified to be in accord with dimensionless distribution (when the cross-sectional average voidage was larger than 0.9900), was influenced by the superficial gas velocity and static bed height. In the upper riser, the mean particle diameter varied little along the radial direction while decreased along the axial direction. In addition, it was verified that the current experimental data coincided well with the operational results of the Baima 600 MW supercritical CFB (SCCFB) boiler. Implications of the experimental results for the design and operation of SCCFB boilers were discussed.