Pesticides are major contributors to environmental pollution, and widely distributed in aquatic environments. Zooplanktons, including rotifers, especially Brachionus calyciflorus Pallas and B. plicatilis Müller, are frequently used as test animals to detect aquatic contaminants because of their sensitivity, specificity of life history and ecological importance. In order to assess the effects of pyrethroids on reproduction of rotifers, and screen out endpoints to detect those aquatic contaminants, the effects of different concentrations of cypermethrin (31.25, 62.5, 125, 250, 500, 1000 and 2000 μg/L) and deltamethrin (15.63, 31.25, 62.5, 125, 250 and 500 μg/L) on population growth rate, ratio ovigerous females/non-ovigerous females, ratio mictic females/amictic females, mictic rate, fertilization rate of mictic females and resting egg production of Guangzhou strain of B. calyciflorus were studied by means of 3-day population growth and 4-day resting egg production tests. The results showed that the cypermethrin concentration affected significantly population growth rate, ratio ovigerous females/non-ovigerous females, ratio mictic females/amictic females, mictic rate and resting egg production (all the P<0.001), but did not affect fertilization rate of mictic females of the rotifers (P>0.05). The deltamethrin concentration affected markedly population growth rate, ratio mictic females/amictic females, mictic rate and resting egg production (all the P<0.05), but did not affect ratio ovigerous females/non-ovigerous females and fertilization rate of mictic females of the rotifers (P>0.05). Compared with the controls, cypermethrin at 31.25-125 μg/L and deltamethrin at all the concentrations except 31.25 μg/L increased significantly the population growth rate of the rotifers, but the reverse was also true for cypermethrin at 1000 and 2000 μg/L. Cypermethrin at 500 μg/L increased significantly the ratio ovigerous females/non-ovigerous females, but deltamethrin at each concentration did not significantly affect it. Cypermethrin at 62.5 and 125 μg/L increased significantly the ratio mictic females/amictic females, but the reverse was also true for deltamethrin at 15.63 μg/L. Cypermethrin at 62.5-250 μg/L increased significantly the mictic rate in the rotifer populations, but cypermethrin at 500-2000 μg/L and deltamethrin at 15.63, 31.25, 250 and 500 μg/L decreased markedly it. Cypermethrin at 62.5 and 125 μg/L and deltamethrin at 15.63 and 125 μg/L increased significantly resting egg production of the rotifers. The fertilization rates of mictic females of the rotifers exposed to all the tested compounds and the controls were zero. In the range of experimental concentrations, significant dose-response relationships existed between the population growth rate, the ratio mictic females/amictic females as well as the mictic rates in the rotifer populations and the cypermethrin concentration. The above-mentioned reproduction parameters of the rotifer B. calyciflorus might be used to detect cypermethrin in aquatic environments. Hovewer, no significant dose-response relationships existed between any reproduction parameters of the rotifer B. calyciflorus and the deltamethrin concentration, indicating there was no feasible to use reproduction parameters of the rotifers to detect deltamethrin in aquatic environments.