Velocity, and residence time distributions play, a crucial role in the performance of microreactors for chemical synthesis. The specific features of fluid flow through multi-plate microchannel reactors are examined by an approxyimate pressure drop model whose validity is confirmed through comparison with more detailed finite-volume calculations. The model results allow for determination of the influence of the geometrical characteristics of the microchannel structures on the flow distributions and are used to optimize the reactor design for maximum flow uniformity.