Split-root solution culture was used to study the promoting effect of lanthanum on rice (Oryza sativa) growth and its physiological mechanisms. Results show that low concentration (0.05～1.5 mg*L-1) increases rice yield and grain numbers. High concentration depresses grain formation (9～30 mg*L-1) and root elongation (1.5～30 mg*L-1). No significant influence on straw dry weight was found over the whole concentration range except the 0.05 mg*L-1 treatment. With the increase of La concentration from 0.05 to 0.75 mg*L-1, catalase (CAT) activity in the first fully expandeing leaves and roots decreases. When La concentration is greater than 0.75 mg*L-1 or less than 9 mg*L-1, it significantly decreases superoxide dismutase activity (SOD) in the leaves and roots. No significant effects were found on chlorophyll, protein and malondialdehyde (MDA) content. Possible mechanisms of La′s promoting effect on rice growth and reduction effect of *O-2 were discussed.