A study quantifying the effects of different copper (Cu) concentrations (50, 200, 800 and 1,000 mg kg⁻¹ Cu) on Cu bioaccumulation and physiological responses of Spartina alterniflora was conducted. Plant biomass and Cu accumulation were determined. Plant height, tiller number, chlorophyll, leaf electrolyte leakage rate (ELR), malondialdehyde (MDA), proline, soluble sugar, and organic acids were also measured. The results showed that S. alterniflora mainly accumulated Cu in fine roots. No significant changes of biomass of fine roots were detected except for obvious reduction under 1,000 mg kg⁻¹ Cu. In leaves, rhizomes and fine roots, the highest Cu accumulations were detected under 800 mg kg⁻¹ Cu. The highest Cu accumulation in stem was revealed under 200 mg kg⁻¹ Cu. Plant height decreased under 1,000 mg kg⁻¹ Cu; chlorophyll content reduced under >50 mg kg⁻¹ Cu; levels of ELR and MDA increased under >200 mg kg⁻¹ Cu. However, osmotic components such as proline and soluble sugar were accumulated to cope with higher Cu stresses (800 and 1,000 mg kg⁻¹ ). Further, oxalic and citric acids were positively related with Cu contents in leaves and stems, suggesting that oxalic and citric acids may be related to Cu detoxification in aboveground parts of S. alterniflora. However, in above and belowground parts, no detoxification function of ascorbic and fumaric acids was observed due to unchanged or decreased trend under Cu stress.