The effects of various concentrations of NiSO4 (0-60 μM) on the activities of cell-wall peroxidase against ferulic acid (FPOX) or syringaldazine and phenylalanine ammonia-lyase (PAL) and the content of lignin in root of rice seedlings were investigated. NiSO4 was found to inhibit root growth and this inhibition was pH independent. NiSO4 was also found to increase the activities of FPOX and syringaldazine peroxidase and the content of lignin in roots. However, NiSO4 did not affect the activity of PAL, the first enzyme of phenylpropanoid pathway. Results suggest that cell-wall stiffening and lignifications are the processes that are enhanced by NiSO4 to reduce growth of rice roots.