The synthesis of Au/Pt and Pt/Rh nanoparticles in microemulsions by a one-pot method has been studied by computer simulation using stoichiometric and in-excess reducing agent. Our study demonstrates that Pt is reduced faster in the presence of Rh than in the presence of Au, and this acceleration is attributed to the higher availability of reducing agent in the Pt/Rh than in Au/Pt synthesis. Final bimetallic nanoparticles show a better metal segregation in Pt/Rh when compared with Au/Pt nanoparticles. In Au/Pt synthesis, Pt reaction rate depends on the ease with which reactants can be exchanged between micelles and the availability of reducing agent. When Pt/Rh nanoparticles are synthesized using a rigid film, the slow intermicellar exchange runs together with the slow reduction rates of the metals. It results in a very slow consumption of reducing agent, so the amount of reducing agent does not affect Pt reaction rate.