Nowadays, soil pollution by Ni²⁺ is getting more severe in some place of China. Nickel (Ni) is an essential microelement of plants, however, large Ni²⁺ accumulation in crops leads to necrosis of plant leaf, lignification of stem and growth inhibition of root. The mechanisms of the Ni²⁺ toxicity are not well understood for nitrogen metabolism of higher plants. In this study, pot culture was conducted to investigate the effects of Ni²⁺ on the growth of roots and shoots, biomass, the uptake and accumulation of Ni²⁺, the contents of nitrate nitrogen, ammonium nitrogen, free proline and soluble proteins, the nitrogen metabolism key enzymatic activities including nitrate reductase (NR), glutamine synthase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH) in four genotypes (13-36, B-7, Jingu 51, Jingu 52) of foxtail millet (Setaria italica (L.) Beauv) seedlings from Shanxi, China. The foxtail millet seeds were cultured in incubators at 26℃ for germination with no light, then planted in the pots spiked with five different Ni²⁺ concentration, namely 25, 50, 100, 150, 200 (mg/kg). The experimental results showed that with the rise of Ni²⁺ concentration the root length, shoot length and biomass declined and the accumulation of Ni²⁺ increased gradually, which formed a sharp contrast with the control group (P < 0.05). In the range of test Ni²⁺ concentration, the content of nitrate nitrogen, the activities of NR, GS, GOGAT of four genotypes of foxtail millet characterized by increasing at low concentration (25-50mg/kg) and declining at high concentration (50-200 mg/kg). The activities of NR, GS, GOGAT reached the peak values when exposed to 50mg/kg Ni²⁺. The nitrate nitrogen contents and NR activities in 13-36 were higher than other three genotypes (P < 0.05). The activities of GS and GOGAT in 13-36, B-7, Jingu51 were 1.69, 1.47, 1.19 and 2.84, 1.03, 3.17 times than those of control group in 50mg/kg Ni²⁺ exposure. However, The GDH activities decreased when the Ni²⁺ concentration higher than 100mg/kg. Ni²⁺ treatments increased the accumulation of ammonium nitrogen in range of 50 to150 mg/kg in the leaves of four foxtail millet and were 1.14 to 3.02 times than control group. Besides these, with the increasing of Ni²⁺ concentration, the content of free proline increased, the soluble protein decreased. Synthesize the above results, we found that Ni²⁺ treatments impaired N assimilation in foxtail millet seedlings by restraining the absorption of nitrate nitrogen and inhibiting the activities of NR, GS and GOGAT, which lead to nitrogen metabolism disturbance. And the toxicity effect was different among different genotypes of foxtail millet. Further, Ni²⁺ stress inhibited the growth of foxtail millet. The tolerance order of four foxtail millets to Ni²⁺ was 13-36 >B-7 >Jingu51 >Jingu52.