The US president tried to quote Mark Esper in a tweet, but instead he referred to him as “Mark Esperanto”.
He wrote: “Mark Esperanto, Secretary of Defense, “The ceasefire is holding up very nicely. There are some minor skirmishes that have ended quickly.”
In a rambling conclusion the president added “USA soldiers are not in combat or ceasefire zones. We have secured the Oil. Bringing soldiers home!”
Mr Esper was sworn into the role in July 2019, after the defence secretary post remained vacant for seven months.
Mr Esper is now at the heart of one of Mr Trump’s most controversial foreign policy decisions.
Earlier this month the US president abruptly announced that troops would leave northern Syria.
Days later, Turkey began to invade the area and started an offensive against Kurdish fighters – who had previously led the struggle against Isis, alongside members of the US military.
American vice president was subsequently forced to broker a ceasefire in the region.
Both side have since accused the other of breaching this truce.
Mr Trump has been also criticised by members of his own Republican party over the decision to withdraw troops.
“Withdrawing US forces from Syria is a grave strategic mistake. It will leave the American people and homeland less safe, embolden our enemies, and weaken important alliances,” Senate majority leader Mitch McConnell wrote in a Washington Post opinion column.
The controversy came as Mr Trump struggles with an impeachment inquiry and plummeting approval ratings.