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Anthropogenic activities such as industrial production, mining, agriculture and transportation are among the main causes for the increase of trace metal concentrations in the environment, especially in water bodies. In this study, we evaluated the chronic impacts of lead (Pb) and arsenic (As) on Daphnia magna, a crucial organism to aquatic ecosystems, at several concentrations (0, 5, 25, 50, 150 and 250 μgl-1 of Pb and 0, 5, 25, 50 μgl-1 of As) for 21 days. The organism’s life history traits, including survivorship, maturation, and reproduction, were recorded daily. In addition, the survival rate of the offspring exposed to 50 μgl-1 Pb was also recorded when the animals were raised in (i) a Pb containing medium and Pb-free medium for 8 days. The results showed that As, at all the test concentrations, did not only negatively affect the survival and cause a delay the maturation, but also reduced the reproductive performance of the animal, especially at the highest concentration. Compared to the control, the survivorship and reproduction of the D. magna exposed to Pb at the highest concentrations (150 and 250 μgl-1) declined dramatically, and it took a longer time to reach maturity. On the other hand, almost all of the recorded life history traits of the organisms exposed to 5, 25 and 50 μgl-1 of Pb were relatively similar to those from the control. However, Pb at the concentration of 50 μgl-1 had detrimental effect on survival of Daphnia’s F1 generation after the 8-day experiment. An abnormality of the metal-exposed D. magna was also observed. An impairment of the daphnids was observed upon exposures to As and Pb at concentrations within the Vietnam guideline values for surface water safety. Hence, further investigations are suggested to adjust the guidelines related to As and Pd for the protection on environmental quality and ecological health.