Effects of particle properties on the rise of single bubbles in a liquid-solid fluidized bed are studied by focusing on the particle-shape effect at various bed voidages near incipient fluidization of glass beads and sand particles. Experiments, covering the bubble-size range 6-37 mm and solids holdups as high as 0.94 times that in tile packed state, are conducted in a 2-D column to directly observe the possible relationship between the rate and tortuous path of bubble rise. The shape effect, being significant when the close-range (surface-to-surface) interactions between the particles are predominant, is appreciable for the relative solids holdups exceeding 0.9. Marked reduction in the bubble rise velocity is observed as the bubble size is decreased below 8 and 12 mm for the spherical glass and irregular sand particles, respectively, This anomalous reduction stems partly from the tortuousness in the rise path and partly! from thr "hesitation" in the net vertical movement. The former, in particular, is quantified ill terms of the tortuosity of the 2-D rise path. The results support the peculiar trend in the rise velocity observed especially for the sand particles.