Ben Wallace revealed he became suspicious and then terminated the call after “several misleading questions”.
The defence secretary has now ordered an immediate inquiry to find out how the impostor was able to speak to him.
He said: “Today an attempt was made by an imposter claiming to be Ukrainian PM to speak with me.
“He posed several misleading questions and after becoming suspicious I terminated the call.
“[It was] a desperate attempt.”
Mr Wallace revealed he had been targeted by the hoax call in a Twitter post.
The fact that a hoax caller was able to speak directly to the defence secretary raises security questions, particularly given Mr Wallace’s suggestion that Russia was behind it.