Luca Attanasio, 43, died in hospital on Monday after the United Nations convoy he was travelling in came under fire near Goma, a statement said.
The convoy reportedly belonged to the UN's World Food Programme (WFP).
An Italian military police officer travelling with the envoy and a Congolese driver were also killed.
"It is with deep sadness that the foreign ministry confirms the death, today in Goma, of the Italian ambassador," the ministry's statement said.