This study has investigated the particle transmission efficiency through the nozzle of the API Aerosizer(TM) numerically. Two-dimensional flow field in the nozzle was first simulated. Particle trajectories for both liquid and solid particles were then calculated to obtain the particle transmission efficiency under various conditions. This study shows that particle aerodynamic diameter, particle materials, particle density and laser beam diameter influence the transmission efficiency. The transmission efficiency is found to increase with increasing particle diameter when the particle aerodynamic diameter is less than several micrometers. The efficiency for liquid particles drops significantly when particle aerodynamic diameter increases from several micrometers because of particle impaction loss in the nozzle. For solid particles, the relationship of the efficiency with particle diameter is found to be more complicated. For particles less than several micrometers in aerodynamic diameter, solid particles behave similarly to the liquid particles. However, as particles are greater than several micrometers, the effect of solid particle bounce is to increase the transmission efficiency with increasing aerodynamic diameter until particles become large enough so that plastic deformation occurs in the particles. Then the transmission efficiency will decrease with increasing particle aerodynamic diameter.