Spraque-Dawley(SD)big rats with weaning weight of (195±15) g were randomly divided into 4 groups with 8 males and 8 females each group. One group drank de-ionized water served as control and also used for analysis with the background. The other three groups were cultured for five months by drinking de-ionized water with 3.0, 4.5 and 6.0 mg·L-1 Sm (NO3)3, respectively. Compared with the rats in control, it is found that the organs of the treated rats are apparently pathologically changed, such as liver swell, lung intumescence, peritoneum conglutination and hardness. Especially, in the high Sm group, the pathological percentage in liver and lung is up to 30%. The pathological changes in liver and lung show that rare earth Sm does hazard biological effects to animals. With increasing Sm concentration, the weight rate of organ/body has a tendency of increasing; the activity of superoxide dismutase (SOD) in liver and kidney decreases, but the maglonydiadehyde (MDA) concentration increases, indicating the abilities of anti-oxidation and the lipid per-oxidation inhibition degenerate, which leads to hard pathological changes in organs. Moreover, the relative weight rate of organ/body, the activity of SOD and the MDA concentration are remarkably lager in liver than in kidney and other organs, suggesting that the biological effect of Sm on liver is the greatest and Sm has a high affinity for liver.