To evaluate the physical bioturbation on tidal flat by the burrowing activity of <i>Ilyoplax pusilla</i> and <i>Scopimera globosa</i>, collapsed and renewed rates of the burrows, population densities and carapace widths, and correlationship between burrow physical parameters and crab carapace widths were investigated on the Banzu tidal flat. Burrowing activity of the crabs developed new ground surface on the inside face of borrows. Therefore, a ground surface area of tidal flat was increased 31.9 % by <i>I.pusilla</i> and 16.5 % by <i>S.globosa</i>, respectively. Soil-turnover rates induced by burrowing activities were found to be 7331 cm<sup>3</sup>/m<sup>2</sup>/month in <i>I.pusilla</i> and 9119 cm<sup>3</sup>/m<sup>2</sup>/month in <i>S.globosa</i>, respectively. This indicates that 11 % and 13 % of the soils from surface to a depth of burrow bottom were turned over by <i>I.pusilla</i> and <i>S.globosa</i> respectively for a month.