Solids volume concentration and solids velocity were determined in an 8.5 m high circulating fluidized bed (CFB) riser with two types of bubble-cap distributors by applying a capacitance probe. In the bottom region of CFB, the solids volume concentration in the centre region is low, while solids concentration increases significantly towards the wall with the highest solids concentration at wall approaching the value at the packed bed. Furthermore, solids volume concentration at high-pressure drop of a bubble cap is lower than that at low-pressure drop of a bubble cap at all lateral positions. The pressure drop of the distributor has little influence on the profiles of solids volume concentrations and on the profiles of solids velocities in CFB upper dilute region. It has been found that the pressure drop of the distributor has little influence on the axial apparent solids concentration in upper dilute region and on the external circulation rate. (C) 2007 Elsevier B.V. All rights reserved.