The effect of static pressure variation at a downcomer bottom, P-do, on axial bed density (ABD) distribution in a riser was examined in a circulating gas fluidized bed system consisting of a 0.1 m i.d. and 10.0 m high riser, a 0.2 m i.d. and 8.2 m high downcomer and a screw feeder between them. The ABD distribution and P-do were determined from simultaneous measurements of static pressure distributions in the riser and the downcomer at a fixed superficial gas velocity of 1.3 m.s(-1) as a function of the circulating solid flux, G(s), and the initial height of solid particles in the downcomer, H-sd, employing 0.054 mm FCC particles as a bed material. For most combinations of G(s) and H-sd, no essential effect of the variation of P-do was found on steady-state ABD distributions. The distributions depended appreciably on P-do only when G(s) takes a certain value where a dense region appears in the lower part of the riser. Under such conditions, a fluctuation of the height of the lower dense region was observed in correspondence to a transitional change in the pressure distribution in the downcomer. In addition, the steady-state dense region height was found to increase with the static pressure at the downcomer bottom which was varied through the change of H-sd and by aeration to the downcomer bottom.