The phytotoxic activity of pyriftalid ([RS]-7-[4,6-dimethoxypyrimidin-2-ylthio]-3-methyl-2-benzofuran-1[3H]-one) on barnyard grass (Echinochloa oryzoides) seedlings emerging from various depths in the soil was investigated in relation to its behavior in the soil. The growth of the barnyard grass seedlings in the soil mixed with pyriftalid was inhibited, depending on the concentration of the herbicide in the soil water but not on the amount in the total soil. A topmost pyriftalid-treated layer was formed by applying the herbicide to the soil surface under water-leakage conditions. The concentration of pyriftalid in the soil water and the amount that was adsorbed on the soil solid decreased with time, but the decrease was more marked in the pyriftalid concentration in the soil water than in the amount that was adsorbed on the soil solid. The emergence time of barnyard grass in the soil was faster in the seeds that were located in the shallower soil layer, compared to the deeper soil layer. The growth inhibition of the barnyard grass seedlings emerging from the shallower soil layer was greater than that of the barnyard grass seedlings emerging from the deeper soil layer after the soil surface application of pyriftalid. It is suggested that the emergence timing from the different soil depths is an important factor affecting the herbicidal activity of pyriftalid when it is applied to the soil surface under paddy field conditions.