In this study, a method was developed to estimate accurately the chloride threshold value for corrosion initiation in reinforced concrete. In this method, chlorides are supplied through a part of the specimen surface, and half-cell potential between the rebar and reference electrode embedded in a concrete specimen was measured in every ten minutes. A sudden drop of half-cell potential was observed as the continuation of the measurement. At that time, the specimen was broken and corrosion of rebar on its narrow surface was confirmed. The chloride threshold value can be estimated by determining the chloride concentration at the time of the potential drop. The estimated chloride threshold values for normal Portland cement concrete with cement content between 254 and 446 kg/m³ are in the range of 1.6 to 3.6 kg/m³. This paper is an English translation from the authors’ previous work [Horiguchi, K., Yamaguchi, T., Maruya, T. and Takewaka, K., (2015). “A study on the method of measuring the chloride threshold value of corrosion and on the estimation of the values.” Journal of JSCE, Ser. E2, 71(2), 107-123. (in Japanese)].