Toxic effects of tribromomethane (TBM), a most used drinking water disinfection byproduct, on rotifers are unknown. we investigated the effects of TBM (0, 0.001, 15, 30, 45, 60, and 75 mg/L) on the life table demography of the freshwater rotifer, Brachionus calyciflorus, fed with three densities (1.0, 2.0, and 4.0 × 10⁶ cells/mL) of Scenedesmus obliquus. It showed that the TBM exposure decreased survivorship and fecundity of the rotifer and significantly affected the developmental stages and life table demographic parameters of B. calyciflorus. Compared with the control, treatments with 30-75 mg/L TBM significantly prolonged the juvenile period of rotifer under different algal densities. Treatments with 0.001 and 15 mg/L TBM significantly decreased the net reproductive rate of rotifer under the algal density of 1.0 × 10⁶ cells/mL, while increased and did not affect it under the algal density of 2.0 and 4.0 × 10⁶ cells/mL, respectively. These results demonstrate that TBM is toxic to B. calyciflorus, and the increased algal density can reduce the toxic effects of TBM on rotifers. The current safety limit of TMB in natural water could affect the community structure of organisms in the aquatic system.