Provided is a method of producing a porous glass, including selectively etching a phase-separated glass with an acid solution, in which the method allows a processing time to be shortened and suppresses gel-like silica from remaining and being deposited in pores of a porous portion. The method of producing a porous glass includes: immersing the phase-separated glass in a bath containing an acid solution; setting an angle θ, which is formed by a surface to be porosified of the phase-separated glass and a bath liquid surface, to 10° or more to 90° or less; and irradiating the bath with an ultrasonic wave to etch the phase-separated glass, thereby obtaining the porous glass.