The spinel MnV(2)O(4) is a two-sublattice ferrimagnet, with site A occupied by the Mn(2+) ion and site B by the V(3+) ion. The magnon of the system, the transversal fluctuation of the total magnetization, is a complicated mixture of the sublattice A and B transversal magnetic fluctuations. As a result, the magnons' fluctuations suppress in a different way the manganese and vanadium sublattice magnetization and one obtains two phases. At low temperature (0,T(*)) the sublattice Mn magnetization and sublattice V magnetization contribute to the magnetization of the system, while at a high temperature (T(*),T(N)), the vanadium sublattice magnetization is suppressed by magnon fluctuations, and only the manganese ions have non-zero spontaneous magnetization. A modified spin-wave theory is developed to describe the two phases and to calculate the magnetization as a function of temperature. The anomalous M(T) curve reproduces the experimentally obtained zero-field-cooled (ZFC) magnetization.