A sampling method sampling a lower-layer liquid from a liquid body comprised of two layers of liquids, an upper-layer liquid (octanol) and the lower-layer liquid (buffer solution), without mixing the layers. An extracting device is provided with a tubular apical end and is adapted to bring the apical end from above into a liquid to extract the liquid through the apical end. The method includes a plug injection step of injecting a plug liquid without mixing with the upper-layer liquid 50a, into the apical end 11a of the extracting device, and an extraction step of extracting the lower-layer liquid with the plug liquid by means of the extracting device.