To provide a method for quickly and accurately judging the presence of coliform bacteria in a food, if required, the number of coliform bacteria.

This method for detecting coliform bacteria by using β- galactosidase as an index and comprises culturing a specimen or a test solution containing a fixed amount of the specimen so as to increase the formed amount of β-galactosidase being a coliform bacteria specific enzyme and measuring the enzyme activity of β-galactosidase. In order to increase the formed amount of β-galactosidase, the specimen or the test solution is cultured in the presence of adenosine 3',5'-cyclic phosphate (cAMP) and/or hexokinase. Preferably the specimen or the test solution is cultured by also using a process for culture in the presence of isopropyl-β-D-thiogalactopyranoside(IPTG) and/or by using a fluorescent substrate having excellent sensitivity to β-galactosidase as (5) a substrate, preferably 4-methylumbelliferyl-β-D-galactoside.