In this study, we investigated the impact of Hg²⁺ and Pb²⁺ on the growth and photosynthetic physiological characteristics of by exposing algal thalli to five concentrations of HgCl2 (0.01 mg/L, 0.025 mg/L, 0.05 mg/L, 0.1 mg/L, 0.25 mg/L, and 0.5 mg/L) and PbCl2 (0.05 mg/L, 0.1 mg/L, 0.5 mg/L, 1.0 mg/L, 2.0 mg/L, and 4.0 mg/L); the reference group exposed to seawater without Hg²⁺ and Pb²⁺. The growth rate, photosynthetic rate, pigment content, chlorophyll Ⅱ fluorescence characteristics, and the activity of RuBisCO and PPDK in the thalli were measured after 7 days of incubation. The special growth rate (SGR) reduced significantly as the Hg²⁺ level increased (<0.05), mortality was observed following incubation with the highest concentration of Hg²⁺, and the photosynthetic rate reduced by 35.48%-77.50%. Similar trends were also observed for chlorophyll a (Chla) and carotenoid (Car) levels (<0.05). Phycoerythrin (PE) and phycocyanin (PC) content was significantly lower at Hg²⁺ levels above 0.1 mg/L (m and Y(Ⅱ) with Hg²⁺ concentration was close to a bimodal curve, and the second peak appeared at 0.05 mg/L;PPDK activity showed a similar trend. The specific growth rate and Chla and Car content was significantly lower at Pb²⁺ levels above 1 mg/L (<0.05). However, no significant change in either chlorophyll Ⅱ fluorescence characteristics or the level in PC content was found among different Pb²⁺ levels. Significantly lower RuBisCO activity was found at the highest Pb²⁺concentration than at lower concentrations, while PPDK activity was significantly higher ( both showed detrimental effects on the growth and photosynthesis of . A stress response was observed after the Hg²⁺concentration reached 0.01 mg/L, and this response increased as Hg²⁺concentration increased, while no stress response was observed at Pb²⁺ concentrations below 1 mg/L.