This paper gives the development status of the embrittlement trend curve (ETC) in Japan. The current Japanese ETC for neutron-irradiated reactor pressure vessel steels, which is standardized by Japan Electric Association Code (JEAC) 4201-2007 (2013 addendum), was developed on the basis of Japanese surveillance and material test reactor data. To improve the accuracy with which the ETC predicts microstructure formation by neutron irradiation, we also used the atom probe tomography data for the ETC revision described in this paper. The revised ETC model (C40 model) has a simple functional form and, unlike the current version of JEAC4201, does not require numerical time integration. The C40 model has a similar transition temperature shift ΔT 41J prediction performance as the current JEAC4201 model and better microstructure formation prediction performance than the current JEAC4201 model. To improve user convenience, we reduced the number of coefficients in the C40 model, obtaining a modified ETC with 20 calibration coefficients (C20 model) that has similar accuracy as the original ETC. The C20 model is being considered as a candidate for the next JEAC4201 ETC. The revision work on JEAC4201 is ongoing within the Japan Electric Association.