The authors found that monodispersed bubbles with a mean diameter of less than 1 mum (monodispersed nano-bubbles) were generated from a porous glass membrane with uniform size-controlled pores. The size of the bubbles generated could be controlled by varying the pore size of the membrane used. When air was permeated through a hydrophilic tubular membrane at a right-angle to the flow of pure water containing sodium dodecyl sulfate (SDS) of 1.7mol(.)m(-3) as a surfactant, and then dispersed into the water phase flowing on the inner side of the membrane, monodispersed bubbles were generated in the pressure region that exceeded the bubble point pressure. Under such conditions, nano-bubbles with a mean diameter of 0.720 mum were generated from a membrane with a mean pore diameter of 0.084 mum. The mean diameter of the bubbles generated was proportional to the mean pore diameter of the membrane used. By contrast, bubbles with a broad size distribution were generated from a hydrophobic membrane, and bubble point pressure was not observed. When the SDS concentration was lower than 1.7mol(.)m(-3), polydispersed bubbles were generated from even the hydrophilic membrane.