The women were struck shortly after 1.30pm on Wednesday while hiking the 3,560ft summit.
The Llanberis Mountain Rescue Team was called to the incident by North Wales police and treated two women at the summit.
A spokesman said one of the women was falling in and out of consciousness with more serious injuries. The other had minor injuries.
Both hikers were evacuated and flown to a hospital in Bangor by helicopter.
The women had been part of a group of five people visiting north Wales.
Rescue coordinator Phil Benbow said they “were very lucky.”
He told the BBC: “As a team we didn’t hang around on the summit or the ridge going down.
“Our advice is when thunderstorms are forecast people should avoid mountain tops, exposed ridges and open flat areas because that is where lightning is most likely to strike.”
The area of Snowdonia experienced tumultuous weather on Wednesday with thunder and lightning, hailstones and clouds.
In England, patients were transferred out of a ward at Trafford General Hospital, Greater Manchester, when it was struck by lightning.
London was also hit with heavy rain on Wednesday following further flooding on Sunday.