The method on combined effects of environmental estrogens and mixture environmental risk assessment was discussed. Batch tests were conducted to assess the in vivo potency of mixtures of estrogens using plasma vitellogenin concentrations in male crucian carp (Carassius carassius) as the endpoint. A nonlinear regression was determined on the concentration response relationship for the single chemical of 17β-estradiol (E(2)), 17α-ethynylestradiol (EE(2)), 4-tert-octylphenol (OP), bisphenol A (BPA), and that of the mixed compounds at equipotent concentrations (E(2)-EE(2), E(2)-EE(2)-OP-BPA), the mixture was tested using a fixed-ratio design. On the basis of statistical selection criteria, the best-fit model is chosen individually for each set of data. Furthermore, the bootstrap methodology is applied for constructing confidence intervals for the estimated effect concentrations. The combined effects of the mixture can be predicted using biomathematical models based on the concentration and potency of the individual mixture components. The finding of non-monotonic dose-response relationship and the combined effects can be accurately predicted in whole range of exposure concentration by the reference models, whereas the outcome of simple effect summation with a great deal of indetermination. Results suggested that there can be a risk of mixture effects. The potential impact of components on mixture would depend predominantly on its concentration, the mixture ratio, and its relative potency. Existing environmental risk assessment procedures are limited in their ability to evaluate the combined effects of chemical mixtures, therefore further improvement is needed.