This study aimed at studying the collection efficiencies of the widely used SKC BioSampler when sampling size-resolved biological viable aerosol particles using an Ultraviolet Aerodynamic Particle Sizer (UV-APS) unit. The test bioaerosols include aerosolized bacterial species and those from indoor air. For optimal performance, different flow rates (Q(sampl)) (5, 12.5 and 20 L/min) and different volumes of collection liquids (V-cl) (5, 10 and 20 mL) were tested for bioaerosol particles from 0.5 to 10 mu m. In addition, the DNA stain method-the LIVE/DEAD BacLight dye and culturing were also utilized to confirm the viable bioaerosol collection efficiencies of the BioSampler. Experimental data showed that when sampling aerosolized Bacillus subtilis at the flow rate of 12.5 L/min, the collection efficiency of the BioSampler decreased from 82.7% (at V-cl=20 mL) to 24.8% (at V-cl =5 mL). The results from the BacLight dye and culturing performed for the samples collected by the BioSampler achieved similar conclusions. When sampling indoor air particles, the overall collection efficiencies of all viable biological particles were 95.3%, 87.7% and 65.5%, respectively, for V-cl = 20 mL, 10 mL and 5 mL at the flow rate of 12.5 L/min. When Q(sampl) was 20 L/min, the BioSampler performed better with V-cl = 5 mL than other volumes. The results from this work suggest that the sampling flow rate plays a dominant role in the overall physical collection efficiency while the collection volume is crucial in preserving the viability of bioaerosol particles. Different from general practice, the operating parameters for the BioSampler should thus be adjusted respectively for target viral, bacterial and fungal aerosol particles.