In this study, our point of view is to generate monodisperse fiber aerosols stably from liquid suspension by using an ultrasonic nebulizer. To fulfill this purpose, we set standard operating conditions in advance by measuring relative humidity of the air flowed from the apparatus, and then generated three kinds of fiber aerosols (potassium titanate whisker, amosite, chrysotile) to investigate this method. The results which were obtained are as follows. 1) Nebulizing method is useful for generating fiber aerosols stably. The longest term obtained in stable generation was as much as 6 hours, and the count median length (CML) of the fibers were 1-2 micrometer. 2) The aerosol concentration ranged from 0.2 to 3.4 mg/m3, and the flow rate of carrier air was found most effective to control aerosol concentration and length. 3) To shift the concentration of liquid suspension was not always effective to shift the aerosol concentration, and too much concentrated suspension tended to cause fiber co-aggregation. 4) Primary fiber sample should be fine to generate fiber aerosol stably, because large-sized fibers will disturb the aerosol generation.