Abstract: Rice cultivars “Liangyoupeijiu”, “9311” and “Shanyou63” were used to investigate the activities of glutamine synthetase (GS), glutamic acid-pyruvic acid transaminase (GPT), glutamic acid oxaloacetate transaminase (GOT), glutamate dehydrogenase (GDH) and protease in rice root during the late development stage. Also the content of soluble protein and free amino acids in rice root, and that of sugar and free amino acids of root bleeding-sap of rice after blooming were analyzed. The results show that GPT and GDH activity peak precedes blooming while that of GS and GOT occurs after one and two weeks of blossom in “9311”. In “Liangyoupeijiu”, GPT, GDH and GOT activity peaks in the first week after blooming while that of GS occurs before blossom. In “Shanyou63”, the four enzymes reach their highest activity two weeks after blossom. The content of soluble protein and free amino acids in “9311” and “Liangyoupeijiu” peaks in the first week after blossom while that in “Shanyou63” delays to the second and third weeks. Peak of root bleeding-sap occurs in the second week after blossom in “Liangyoupeijiu”, which is one week earlier than in “9311” and “Shanyou63”. Peak time difference between bleeding sap and free amino acids in roots is one week, but the lag-time is different for the three cultivars — one week for “Liangyoupeijiu”, two weeks for “9311” and insignificant for “Shanyou63”. Bleeding-sap sugar content in “Shanyou63” is remarkably higher than in the other two cultivars (P<0.01), while the content of free amino acids in “9311” is significantly higher than in the other two cultivars (P<0.05). It is inferred from the results that nitrogen metabolism in “Liangyoupeijiu” peaks earlier, but at a lower value than in the other two cultivars. This indicates an earlier decline in root physiological activity at late development stage in “Liangyoupeijiu” than in the other two cultivars. Notable differences exist in the strength and peak time of metabolism among the three cultivars. Tissue metabolism and bleeding-sap peak occurs at different times and with different strength, and at varying time-lags among the cultivars.