Fertilization is an important agricultural strategy for enhancing the efficiency of phytoremediation in copper (Cu)-contaminated soils. In this study, the effects of nitrogen (N) forms, including ammonium (NH4+-N) and nitrate (NO3--N), on the growth, translocation, and accumulation of Cu in the tissues of Ricinus communis L. were investigated in pot and hydroponic experiments. The results demonstrated that higher biomass and N contents in plants were obtained when N was supplied as NO3--N rather than NH4+-N. Application of N increased the Cu content in the roots of R. communis, with a higher content after NH4+-N (53.10-64.20 mg kg-1) than NO3--N (37.62-53.75 mg kg-1) treatment. On the contrary, the levels of Cu translocation factors were much higher in NO3--fed plants (0.34-0.45) than in NH4+-fed plants (0.28-0.38). The suggested amount of N for fertilizer application is 225 kg hm-2, which resulted in the highest Cu content in R. communis and optimal plant growth. As the main Cu-binding site, root cell walls accumulated less Cu in plants treated with NH4+-N compared with NO3--N. Additionally, NH4+-N induced a higher malondialdehyde content and more severe root damage compared with NO3--N. In the leaf, a larger number of black granules, which could be protein and starch grains involved in the detoxification of Cu in R. communis, were present after NH4+-N than NO3--N treatment. These results illustrate that N forms are especially important for Cu translocation and accumulation and that immobilization and transformation of Cu in roots were improved more by NH4+-N than NO3--N. In conclusion, N fertilizers containing the appropriate forms applied at suitable rates may enhance the biomass and Cu accumulation of R. communis and thereby the remediation efficiency of Cu-contaminated soils.