The present study investigated the arsenic (As) remediation potential of barnyard grass (Echinochloa crus-galli L. Beauv. var. formosensis Ohwi), with a special focus on the behavior of As in the soil in comparison with rice (Oryza sativa L. cv. Nipponbare). For both plants, very little growth inhibition was observed in the As-contaminated soil. The amount of As in the soil was reduced by the plant's uptake and the level of As in the soil water from the rice-growing pots was remarkably lower than that in the plant-free soil water. In the soil with the barnyard grass, the amount of As in the soil water was higher than that in the plant-free soil water, but the amount of As in the soil and the amount of As that was adsorbed on the soil solid were reduced by the plant's uptake. At the highest As level in the soil (100 mg kg−1), 249.60 and 101.26 µg As pot−1 were taken up by the rice shoot and barnyard grass shoot, respectively, and total amounts of 1468.65 and 1060.57 µg As pot−1 were taken up by the barnyard grass and rice seedlings, respectively. At the same As level in the soil, the As concentrations were 14.99 and 37.76 µg g−1 in the shoot of barnyard grass and rice, respectively, and 486.61 and 339.32 µg g−1 in the root of barnyard grass and rice, respectively. Barnyard grass took up more As than rice, but the As concentration in the shoot of barnyard grass was lower than that in the shoot of rice. A considerable amount of As was taken up by both barnyard grass and rice, suggesting that the plant species have the potential to remediate As-contaminated soil.