Fryatt struck on 53 minutes when he latched on to a floated pass from Richie Wellens and blasted the ball beyond Luke Steele from seven yards.
The game got off to a slow start with the best chances falling to Robbie Neilson who headed tamely at the goalkeeper and to Lloyd Dyer, who was within a whisker of connecting with Dany N'Guessan's cross.
City were given a scare at the other end when Steve Foster headed an Iain Hume corner narrowly over before Dyer dragged a low shot wide of the post.
Chris Weale was called into serious action for the first time on 32 minutes when he had to get down smartly to palm aside Martin Devaney's fierce drive.
Leicester then squandered a great chance when Fryatt scuffed a shot against Steele from seven yards after a Wellens cross had left him one-on-one with the keeper.
The Foxes picked up the pace after the restart and almost broke the deadlock on 51 minutes when Steele was at full stretch to keep out a Neilson header with Anderson Silva blocking Fryatt's follow up shot.
Then came Fryatt's goal and there almost followed another moments later, when Jack Hobbs headed a Paul Gallagher corner into the sidenetting.
Wayne Brown snuffed out a rare Barnsley chance on the hour mark when he slid in to block Andy Gray's close-range shot after good work by Jamal Campbell-Ryce.
Steele then conjured up two superb saves in as many minutes to keep out fierce drives from first Gallagher and then N'Guessan.
But there were moments when City looked vulnerable at the back and they had a scare late on when Barnsley substitute Rob Kozluk saw his angled shot drift just wide of the far post.