This study has been conducted to investigate the pumping characteristics of diffuser-nozzle based thermopneumatic micropumps with different input voltages and frequencies. In this study, the displacements of the membrane have been obtained changing the input voltage and frequency in load-free state because it is very difficult to measure the displacement of the membrane in an actual load state. It has been found that the amplitude of the membrane displacement increases as the input voltage increases. The pressure head of the thermopneumatic micropump increases almost linearly over some range of the input voltage and decreases almost linearly as the frequency increases. Also, the results show that the thermopneumatic micropump can pump the fluid over a certain input voltage. This study can be utilized as basic data for design and evaluation of thermopneumatic micropumps.