Yield of swamp rice on acid sulphur soil was increased by liming and could be related to soil pH but was unaffected by drainage and differences in H2S in the soil. The seedling stage was most sensitive to acid and yield could be dramatically improved by planting mature vigorous seedlings. Survival of seedlings, tillering and panicle formation were the most important yield components affected by liming and acidity. Liming also increased spikelet number and grain size to a lesser degree. The optimal economic lime level for 3-week seedlings was around 4 t/ha but could be lower with 5-week seedlings.