With Free-Air CO2 Enrichment(FACE) technique, this paper studied the root activity and amino acid(aa) synthesis of rice (Oryza sativa )at low N(LN, 150 kgN x hm(-2)) and normal N(NN, 250 kgN x hm(-2)) under ambient air and elevated atmospheric CO2 (Ambient + 200 micromol x mol(-1)). Under elevated CO2, the xylem exudates per hill changed little, while the xylem exudates per stem declined by 1.4% - 21.7% as the result of greater tiller numbers. At tillering and heading stages, elevated CO2 increased aa N/inorganic N in xylem exudates by 11.1% - 143.1%, but did not affect the aa concentration in xylem exudates and the total amount of aa in roots significantly. However, at 35 days after heading, the aa N/inorganic N ratio decreased by 38.1% (LN) and 29.2% (NN) under elevated CO2. FACE also declined the aa concentration in xylem exudates by 34.0% (LN) and 44.7% (NN), and the total amount of aa by 50.8% (LN) and 40.0% (NN), which meant the retarded capability of aa synthesis in roots. N amendment led to a decrease of aa N/inorganic N in xylem exudates by 19.5% (Ambient) and 36.8% (FACE) at heading stage, as the result of unaffected aa and increased inorganic N concentration. There existed a significantly antagonistical CO2 x N interaction on aa N/inorganic N at heading stage.