Abstract: The number of microorganisms in domestic drinking water is one of the important monitoring items for water quality safety. To verify the understanding of domestic testing laboratories for the measurement of Escherichia coli (E.coli) in drinking water, the National Institute of Metrology (NIM) developed a proficiency testing sample for the quantification of E.coli in drinking water and carried out a proficiency testing to assess the ability of participating laboratories. Complied with the national standard GB/T 5750.12-2006 Standard examination methods for drinking water - Microbiological parameters, 11 laboratories participated in the proficiency testing and determined the CFU or MPN value of E.coli in lyophilized samples reconstituted in sterile water by using the filtration membrane method and enzyme substrate method. The statistics indicated that the results of all the participating laboratories are satisfactory. The E.coli quantitative proficiency testing samples are homogeneous and stable, which can meet the requirement of proficiency testing for quantification of E.coli in drinking water and reflect the ability of participating laboratories.