This study has been conducted to investigate flow characteristics of a micropump with piezoelectric materials. In this study, the change of flow rates has been investigated for different positions of the inlet and outlet and for different distances between them. The FSI(Fluid Structure Interaction) method has been employed for numerical analysis of the piezoelectric diffuser/nozzle based micropump. It has been found that time averaged flow rate is greater in the case that distance between the inlet and outlet is longer. For the cases where the positions of the inlet are different with the position of the fixed outlet at the center, the flow rate is increased as the inlet is located farther from the center. This study may supply fundamental understandings for the design and analysis of the prototypes of piezoelectric micropumps.