Algal cultures of Dictyosphaerium sp. were treated with a wide range (0-8 mg/L) of nonylphenol (NP) applications to investigate the species' potential to perform bioremediation of NP-contaminated wastewater and explore the mechanism of NP toxicity in algal cell. The algal species exhibited a high tolerance for NP and efficiently removed even high concentrations of NP. The accumulation of NP in algal cells tended to increase and the percentage of NP adhered to the cell walls tended to decrease as the NP concentration increased. The thylakoid density and the pyrenoid size also tended to decrease as the NP concentration rose. The key genes involved in the antioxidative pathways and photosynthetic pathways were down-regulated in the NP-treated algal cells. Algal ribosome genes were especially sensitive to NP. The results indicated that NP could induce oxidative stress in algal cells and that Dictyosphaerium sp. showed potential as a bioremediation agent.