The point takes Walter Mazzarri's side to within three points of the Rossoneri at the top of the table and cements second place ahead of Lazio, but they would have expected more at the Stadio San Paolo just six days after thrashing Juventus 3-0.
But Fiorentina gave a good account of themselves and deserved a point, which leaves them in mid-table.
Napoli started brightly, but soon faded as the momentum from their win over Juve last weekend quickly disappeared.
The Viola took control of the game and had the first real chance after 31 minutes but Mario Santana failed to test Morgan De Sanctis from close range.
The winger was reluctant to use his weaker right foot and instead swung his left leg at the ball, missing it completely with only the Napoli custodian to beat.
Paolo Cannavaro nearly had a simple tap-in at the other end, but the ball spun away from him and towards Fiorentina goalkeeper Artur Boruc.
Adam Ljajic missed the best chance of the game in the 39th minute when he placed his shot over the crossbar from close to the penalty spot after being picked out by Santana.
Both teams appeared tired, physically and mentally, in the second half and the best opportunity was a shot from Donadel which went inches wide of De Sanctis' right-hand post.
Without the suspended Marek Hamsik, Napoli lost an important dimension to their attack and Edinson Cavani, who grabbed a hat-trick last weekend, did not have a single sight of goal as Napoli were frustrated in their own back yard.