Vunipola, who's made 18 appearances for London Wasps this season, follows team-mate Joe Launchbury as well as Freddie Burns and Dylan Hartley as the latest Aviva Premiership Player of the Month winners.
Vunipola, 20, was selected by a media panel - chaired by Premiership Rugby Communications Director, Paul Morgan - of Stuart Barnes, Alastair Eykyn, Ian Stafford, Nick Mullins, David Rogers, Mick Cleary and Jill Douglas.
He won the award for some stunning performances for London Wasps in December, which earned him a place in England's wider training squad, covering for Tom Croft.
Aviva Ambassador Will Greenwood is one of Vunipola's biggest fans and even though the London Wasps player hasn't won an England cap Greenwood believes he could make this summer's Lions tour.
"Billy Vunipola is a big mover in more ways than one. The Wasps No8 is a young lad whose error count last season was too high and his fitness not good enough," said Greenwood.
"Now he looks like a man, and a big, big one at that. He is an outstanding ball carrier, and he has great hands. His discipline has improved enormously and he has remained very explosive, in a good way. He is not super fit yet, but looking like someone you would consider at international level which has been rewarded by the Saxons berth."
"The No8 slot is not nailed down for England despite Ben Morgan putting in a strong game against New Zealand. Billy is still in this and with performances like he put in December will only ensure he steps closer to England - and even a berth on the Lions."
When Vunipola returns to London Wasps from duty with England he will be presented with a trophy and £500 to give to his chosen charity.