Microparticles play important roles in our life. Besides chemical compositions and morphology, the size of microparticles will also decide their behavior in the environment or in organisms. Weighing the mass of microparticles by mass spectrometry is a useful method to characterize their size. In this technical note, a miniature particle mass spectrometer with an aerodynamic desorption/ionization ion source has been developed. We used a compact main control board to produce an ac voltage for trapping and ejecting the particles. The sampling process and data acquisition were also controlled by this board. We utilized this instrument to measure polystyrene spheres, silica particles, and mice red blood cells. Mass distributions of these particles were obtained rapidly with good accuracy.