Andrew Gray, Curator of Herpetology at Manchester Museum, said venomous snakes in Egypt - cobras or vipers - would have been too large to get unseen into the queen's palace.
He was speaking to Egyptologist Dr Joyce Tyldesley in a new video which is part of an online course introducing ancient Egyptian history.
According to ancient accounts, Cleopatra committed suicide by holding a snake to her breast and allowing it to bite her.
The snake hid in a basket of figs brought in from the countryside, and was also used to kill one or two of her serving maids.
There would also be too little time to kill 2 or 3 people - because snake venom kills you slowly - with in any case only a 10 per cent chance of death.
"Not only are Cobras too big, but there's just a 10 per cent chance you would die from a snake bite: most bites are dry bites that don't inject venom," Gray said.
"That's not to say they aren't dangerous: the venom causes necrosis and will certainly kill you, but quite slowly.
Tyldesley, author of the book 'Cleopatra: Egypt's Last Queen', is a contributor to the free online course 'A History of Ancient Egypt'.
Cleopatra, who died at the age of 39 in 30 BC, was a member of the Macedonian Greek royalty and her family ruled Egypt for more than three centuries.
