Aluminum toxicity is an important growth limiting factor for crop production on acid soils. The effect of five Al concentrations (0, 371, 742, 1484, and 2226 yM) in nutrient solution on the growth and chemical composition of six upland rice (Oryza SatiaL.) cultivars (IAC 1131, Fernandes, Matao, IPEACO 562, IRAT 2, and IPEACO 162) was studied. The concentrations and activities of Al species in the nutrient solution were calculated using the GEOCHEM program. The range in calculated activities of each of the Al monomers was 73 to 411 yM for Al , 7 to 41 μM for Al(OH)2+, 4 to 21 μM for AKOH)2+, 0.07 to 0.41 μM for Al(OH)3°, and 125 to 495 yM for AlSO4+. Aluminum reduced shoot and root growth but the magnitude of the reduction varied from cultivar to cultivar. The cultivar Fernandes was most tolerant and IPEACO 562 most susceptible to Al toxidty of those cultivars tested relative to shoot dry weight. Fernandes also had high P uptake and low Al concentration in the shoot compared to the other five cultivars. The uptake and use efficiency of P was more highly correlated with the growth of rice than the uptake or use efficiency of Ca or Mg.