Amano, 72, was reappointed in 2017 to a third four-year term in charge of the IAEA, until 30 November 2021.
According to a Reuters report, two likely candidates to succeed Amano are Argentina's envoy to the IAEA, Rafael Grossi, and Romania's Cornel Feruta, the IAEA chief coordinator - effectively Amano's chief of staff.
Officials familiar with the matter told Reuters that Amano's health had declined since the IAEA announced in September 2018 that he had undergone an unspecified medical procedure outside of Austria, where the agency is based.
The IAEA chief has frequently stressed that his agency's work is more technical than political, a reaction to the tenure of his predecessor Mohamed el Baradei, who together with the IAEA was awarded the 2005 Nobel Peace Prize and disagreed with US officials over Iran.
Amano's plan to leave before his tenure ends leaves the IAEA's 35-nation Board of Governors time to pick a successor, who must also be approved by the agency's General Conference, a meeting of all member states, according to Reuters. A regular annual meeting of the General Conference is due to be held in September.
"The Director General is in contact with Members of the Board of Governors regarding his future plans. He will make a formal communication to the Board at an appropriate time", the IAEA said Wednesday, cited by Reuters.