The sale is the first in a raft of planned privatisations to reduce Italy's 2-trillion-euro debt pile that will bring cash directly into the state's coffers.
Three financial sources told Reuters that the price guidance for the placement was around 4 euros a share, representing a discount of around 1.2 percent on Wednesday's Enel closing price.
At 0810 GMT shares in Enel were down 1.9 percent to 3.97 euros, underperforming a flat Milan bluechip index.