Seaweed contains many kinds of active substances that have anti-aging bioactivities and rotifers are excellent models for studying the biology of aging. The aim of this study was to examine the effects of various concentrations of extract from the seaweed Gracilaria lemaneiformis (0, 250, 500, 750, and 1000 mg/L) on the life history parameters of the rotifer Brachionus plicatilis, fed two different food types (Chlorella pyrenoidosa and Chlorella vulgaris) at two concentrations (1.0×10⁶ cells/mL and 2.0×10⁶ cells/mL). With a food concentration of 1.0×10⁶ cells/mL of C. vulgaris, G. lemaneiformis extract significantly increased the egg number, life span, net reproductive rate, and generation time of rotifers (P < 0.05), with these parameters reaching their peak at a seaweed extract concentration of 750 mg/L. With a concentration of 2.0×10⁶ cells/mL of C. pyrenoidosa as food, G. lemaneiformis extract significantly increased the life span and net reproductive rate of rotifers (P < 0.05), with the egg number and life span reaching their peak at 500 mg/L. Under the same concentration of G. lemaneiformis extract, the net reproductive rate and generation time of rotifers fed C. vulgaris at a concentration of 1.0×10⁶ cells/mL were significantly higher than those fed with the concentration of 2.0×10⁶ cells/mL; the net reproductive rate and generation time of rotifers fed with C. pyrenoidosa were significantly higher than those fed with C. vulgaris at the concentration 2.0×10⁶ cells/mL. The analysis showed that the interaction between the different concentrations of Gracilaria extract and different kinds of Chlorella had significant effects on the intrinsic rates of B. plicatilis. These results indicate that G. lemaneiformis extract could promote the growth and reproduction of B. plicatilis and extend its life span.