Abstract: The single and combined toxicities of Zn²⁺ and Cd²⁺ have raised concerns in aquatic organisms for many years. However, chronic toxicities of the two metal ions to the population growth of rotifers were seldom known. In the present study, the toxic effects of Zn²⁺ (0.315,0.630 and 1.260 mg/L), Cd²⁺ (0.073,0.145 and 0.289 mg/L), and the combination of Zn²⁺ and Cd²⁺ (0.315 and 0.073,0.63 and 0.145, and 1.260 and 0.289 mg/L) on the population growth rate and the mictic rate of the freshwater rotifer Brachionus calyciflorus were evaluated at three temperatures (15,0 and 25 ℃) and three algae (Scenedesmus obliquus) densities (0.5×10⁶,1.0×10⁶ and 2.0×10⁶ mL-1) using the 3-d population cumulative culture method. The results showed that compared to the controls, the number of the treatments which inhibited the population growth rate of the rotifers increased with the rise of the temperature. At 15 ℃ and 0.5×10⁶ mL-1 of S. obliquus, Zn²⁺ at 1.260 mg/L, Cd²⁺at 0.289 mg/L, and the combination of Zn²⁺ and Cd²⁺at 1.260 and 0.289 mg/L, the population growth rate of the rotifers decreased. At 20 ℃ and the same algal density, five treatments including Zn²⁺ at 0.315 and 1.260 mg/L, Cd²⁺at 0.289 mg/L, and the combination of Zn²⁺ and Cd²⁺at 0.630 and 0.145 and 1.260 and 0.289 mg/L, the population growth rate of the rotifers decreased. However, at 25 ℃ and the same algal density, all treatments reduced the population growth rate of the rotifers. At 15 ℃ and 2.0×10⁶ mL-1 of S. obliquus, all treatments had no effect on the population growth rate of the rotifers. At 20 ℃ and the same algal density, five treatments including Zn²⁺ at 0.630,1.260 mg/L, Cd²⁺ at 0.289 mg/L, and the combination of Zn²⁺ and Cd²⁺at 0.630 and 0.145 and 1.260 and 0.289 mg/L reduced the population growth rate of the rotifers. However, at 25 ℃ and the same algal density, all treatments decreased the population growth rate of the rotifers. At 15 and 20 ℃, and compared to the algal densities of 0.5×10⁶ and 1.0×10⁶ mL-1, the number of the treatments which inhibited the population growth rate of the rotifers decreased at the high (2.0×10⁶ mL-1) algal density. At 25 ℃, the population growth rate of the rotifers increased with the rise of the algal density. At 15 and 20 ℃, and 0.5×10⁶ mL-1 of S. obliquus, and compared to the treatments of Zn²⁺ at 1.260 mg/L and Cd²⁺ at 0.289 mg/L, the combination of Zn²⁺ and Cd²⁺at 1.260 and 0.289 mg/L reduced the population growth rate of the rotifers. At 25 ℃ and 2.0×10⁶ mL-1 of S. obliquus, and compared to the treatments of Zn²⁺ at 0.630 mg/L and Cd²⁺ at 0.145 mg/L, the combination of Zn²⁺ and Cd²⁺ at 0.630 and 0.145 mg/L reduced the population growth rate of the rotifers. These results indicated that the population growth rate of the rotifers was more sensitive to the interaction among temperature, algal density and the concentration of treatments than the mictic rate, and with the rise of temperature and the decline of the algal density, the toxicities of Zn²⁺, Cd²⁺, and the combination of Zn²⁺ and Cd²⁺to the population growth of B.calyciflorus increased.