BACKGROUND Biochar and compost have been proven to have significant positive effect on stabilization of toxic metals in contaminated soil. The aim of this study is to investigate the effect of compost of wheat straw biochar (CB) (4%, 8%, 12% and 18%) with different nitrogen dosages (50, 150, 250 and 300 kg ha(-1)) as amendment on plants growth and mobility and bioavailability of lead (Pb) and copper (Cu) as well as the nutrients in smelter-contaminated soil. RESULTS Diethylenetriaminepentaacetic acid (DTPA)-extractable and total Pb concentration were significantly (P < 0.05) decreased in the CB treated soil compared with the control, especially T14 (12% biochar applied compost with 300 kg ha(-1) nitrogen) dramatically reduced the Pb content by 37.4%. While, the concentrations of total and DTPA-Cu increased in most CB modified treatments, while, the DTPA-Cu concentration of T11 (12% biochar applied compost with 50 kg ha(-1) nitrogen) decreased by 27.3%. Meanwhile, compared with control, the CB amendment significantly improved Chinese cabbage yield and nutrients in soil. CONCLUSIONS Overall, the result suggested that CB could be a useful additive to decrease the bioavailability of Pb and improve plants growth and soil nutrients by reducing the ecological risk of soil contamination. (c) 2019 Society of Chemical Industry