Sand culture was conducted to study the root morphologic characteristics and physiological indices in two rice cultivars with different N use efficiency (NUE), Nanguang with high NUE and Elio with low NUE, under two N rates (1 and 5mmol L-1). The results obtained were listed as follows. Compared to Elio, grain yields of Nanguang were more than 50% under two N rates. Nitrogen and biomass accumulation in rice cultivars increased with increasing N application rates But nitrogen and biomass accumulation of Nanguang were much greater than these of Elio at the latter growth stages.The root morphologic characteristics in high NUE rice cultivar (Nanguang) had more sensitive responses to high N application rates than the low NUE rice cultivar (Elio). Compared to N application rate of 1mmol L-1, root lengths were 127% greater in Nanguang and 92% greater in Elio under N rate of 5mmol L-1; and root surface areas were 114% greater in Nanguang and 82% greater in Elio. Root morphological characteristics of Elio with low NUE rice cultivar, decreased more rapidly than Nanguang after the heading stage. Root bleeding rates of Elio were lower than that of Nanguang at different growth stages. Compared to Elio, root bleeding rate of Nanguang were 11%（1mmol L-1）and 32%（5mmol L-1）greater at jointing stage and 17%（1mmol L-1）and 18%（5mmol L-1）greater at heading stage. It was concluded that efficient N use of rice cultivar depended to a great extent on greater root morphological characteristics and stronger root physiological activity.