The overall yielding behavior of anisotropic composites is affected by the hydrostatic pressure. A method to predict the overall elasto-plastic behavior of composites based on the Mori-Tanaka theory is expanded to examine the normality or the associativeness of the overall flow rule of composites quantitatively. A phenomenological constitutive model is used to evaluate approximately but quantitatively the hydrostatic-pressure effect on the subsequent yielding, and the results are compared with experimental data.