This liquid sterilization method comprises: (1) a step for circulating a liquid to be sterilized, which is a solution or a suspension, through a flow path formed between a pair of parallelly arranged partition walls having therebetween a gap with a predetermined width and (2) a step for irradiating the liquid to be sterilized that passes through the flow path with ultraviolet light from one or two ultraviolet light emitting surfaces provided on either one or both of the two opposing faces of the pair of partition walls, wherein the width, in the direction perpendicular to the ultraviolet light emitting surface, of the gap is less than or equal to the sum total of an effective optical path length of the one or two ultraviolet light emitting surfaces, and the effective optical path length of the ultraviolet light emitting surfaces is defined as the thickness of a layer of the liquid to be sterilized for causing the irradiance of penetrating ultraviolet light to be 0.001 mW/cm2 when the ultraviolet light emitted from the ultraviolet light emitting surface penetrates the layer of the liquid to be sterilized.
