The Mötley Crüe singer appeared in a Las Vegas court to enter the plea on Wednesday, reports TMZ.
Neil was arrested last June and had been charged with driving while intoxicated in Las Vegas.
Police said that his blood alcohol level was almost three times over the legal limit.
The 49-year-old is expected to serve 15 days at the Clark County Detention Centre followed by 15 days of house arrest.
He is scheduled to begin his sentence on February 15.