Cadmium (Cd) is one of the heavy metals whose behavior in ecosystems should be watched because of their toxicity to human health. The Codex Alimentarius Commission decided on maximum levels for Cd in foods (wheat, potato, vegetables etc.) in 2005. To improve resource recycling in Japan we need to promote the application of composted animal manure to arable land. However, animal manure contains very small amounts of heavy metals. Orihara et al. (Jpn. J Soil Sci. Plant Nutr., 2002; 73:403-409) reported that the average Cd content of composted cattle manure in Japan was 0.38 mg/kg. Excessive animal manure application is likely to cause heavy metal accumulation in the soil. We used paddy lysimeters to evaluate the effect of composted cattle manure application on Cd leaching and the Cd content of rice plants. Four lysimeters (0.5 x 1.0 x 0.5 m (H)) were filled with paddy soil from Yawara, Ibaraki, Japan. We applied composted cattle manure at 0, 2, or 6 kg/m2 to each of three of the lysimeters on 14 April 2003 and 18 March 2004. We applied 18 kg/m2 compost to the last lysimeter on the above date in 2003 but not in 2004. Chemical fertilizer was not applied. The lysimeters were flooded by tap water irrigation from mid-May to early September. Ten forage rice seedlings were transplanted into each lysimeter (20 seedlings/m2) in mid-May and the rice was harvested in late September in both year. Leachates were collected every week during the irrigation period and after rain during the unirrigated period. Leachate volume and quality were measured. Heavy rain just after the application of composted manure increased the Cd concentration in the leachate, suggesting that Cd had flowed out of the compost. Under flooded conditions the leachate Cd concentration decreased dramatically, although it increased again after irrigation stopped. The Cd concentration in the leachate changed synchronously with sulfate ion (SO42-) concentration. These observations support the theory that Cd combines with S and is immobilized in the reduced layer of the soil. Analysis of the Cd balance for 2004 revealed that, in the absence of compost application, Cd leached out from the paddy soil in the lysimeter at a rate of 0.2 mg/m2/year. When composted cattle manure was applied, the amount of Cd leaching increased: about 0.3 mg/m2/year leached out from the lysimeters that had received compost at 2 and 6 kg/m2. In contrast, the Cd content of rice plants and the amount of Cd uptake by plant decreased as the rate of application of composted manure increased. The amount of leaching of Cd from the lysimeter that had received Cd at 18 kg/m2 in 2003 but did not receive compost in 2004 was almost the same as that from the lysimeter with no compost in 2004. Application of composted manure increased the amount of Cd leaching but decreased Cd uptake by rice plants. We considered that Cd in the composted manure was washed out by heavy rain just after compost application, but the chelating action of the organic matter in the compost prevented the amount of Cd uptake by the plants. Application of composted manure could be a promising tool for regulating Cd concentrations in rice.