A new method for production of fine Shirasu balloons from glassy volcanic materials, named Shirasu, was developed. Finer-mesh Shirasu balloons were required to supersede conventional Shirasu balloons. However, pulverized Shirasu easily agglomerates and clogs; therefore, it cannot be supplied continuously to a furnace. It was shown that the fluidity and the floodability of the pulverized Shirasu can be improved by application of a dry surface treatment. After surface treatment, fine Shirasu balloons of mean particle size of under 20 mum were successfully prepared in a fluidized sand-bed furnace by rapid heating of the pulverized Shirasu. The foaming characteristics of the fine Shirasu balloons improved after undergoing pre-heat treatment of the pulverized Shirasu in the temperature range of 150-300 degreesC: an increase in pre-heat temperature resulted in a decreased expansion ratio of the fine Shirasu balloons.