Abstract: A method for measuring the number of living microorganisms in a specimen which comprises entrapping the microorganisms on a hydrophobic filter after the dyeing thereof, or alternatively dyeing the microorganisms after entrapping them on the hydrophobic filter, removing excessive coloring matter by washing, and then determining the number of the microorganisms by the degree of coloration thereof. A kit for measuring the number of living microorganisms which comprises a hydrophobic filter, a syringe to which the filter is fittable, a coloring matter solution, a cleaning solution, and a color reference table. The present invention enables the rapid and convenient measurement of the number of living microorganisms in the specimen without use of special equipment. In accordance with the present invention, the measurement is usually completed within ten minutes.