Provide a method for accurately quantifying 4'-GL and galacto-oligosaccharide by separating 4'-GL with ease and at low cost from a sample containing galacto-oligosaccharide and dextrin. A method for detecting and quantifying galacto-oligosaccharide, which is a method for detecting and quantifying galacto-oligosaccharide in a sample containing galacto-oligosaccharide and dextrin, characterized in that the sample is caused to react with a derivatizing reagent to derivatize the dextrin and galacto-oligosaccharide in the sample, after which the galacto-oligosaccharide component in the sample is separated by high-performance liquid chromatography using a C30 reverse-phase chromatography column.
