An axial flow cyclone to remove fine particles at low pressure conditions (6-23 torr) was designed and tested. The inner diameter of the cyclone is 3.0 cm and tested flow rates are 0.455 and 1.0 slpm. A theoretical evaluation was first carried out to calculate the particle collection efficiency and cutoff diameter for the axial flow cyclone. Experiments were then conducted to test the theory at different flow rates, pressures and cyclone designs. It was demonstrated that at sufficiently low pressure of 6 torr (flow rate=0.455 slpm), the axial flow cyclone is able to remove particles below 100 nm efficiently, and the flow Reynolds number was found to have a great effect on the particle collection efficiency.