The Italian champions take the Nerazzurri on at San Siro in Saturday night's Derby d'Italia with both teams unbeaten and with two wins on the board from their opening two games.
"We have a lot of respect for Inter," Buffon told Gazzetta dello Sport. "We fear them.
"They have a great coach in Walter Mazzarri and they are prepared.
"They are a team that can make life difficult for any rival and they will challenge for the Scudetto."
Defeating Juve in the Derby d'Italia would be a major confidence boost for an Inter side that is trying to make up for last season's dismal ninth-placed finish.
That outcome cost coach Andrea Stramaccioni his job and meant Inter missed out on European football in 2013-14.
However, Buffon, whose team open their Champions League campaign at FC Copenhagen next Tuesday, believes that scenario will give Inter the edge.
"They will have the advantage of being able to concentrate on the domestic front," Buffon said.
"But we are very keen to win our third consecutive league title and it's going to be a battle."
AC Milan celebrated their first win of the campaign with a 3-1 triumph over Cagliari last time out.
The Rossoneri will, however, have to overcome the absence of injured defenders Mattia De Sciglio, Ignazio Abate and Matias Silvestre in Saturday's game at Torino.
Napoli are looking to make it three wins in a row when they welcome Atalanta to the Stadio San Paolo.
Roma also have winning momentum on their side as they go up against Parma at the Stadio Ennio Tardini on Monday, with victories against Livorno and Hellas Verona seeing Rudi Garcia's men remain perfect so far.
Bologna face a tough trip to the Stadio Friuli on Sunday when they take on Francesco Guidolin's Udinese.
The Bianconeri have not lost at home in Serie A since September 2 last year.
There will be no better time for Genoa to turn around their dismal start to the season than on Sunday when they face city rivals Sampdoria at the Marassi - with Samp playing the role of designated home team.
Genoa go into the first Derby della Lanterna of the season on the back of two straight defeats.
Lazio fans were left frustrated following their side's 4-1 loss to Juventus two weeks ago and they will expect a drastic improvement when Chievo come to town.
Verona, meanwhile, are hoping veteran striker Luca Toni can recover from injury in time for Sunday's game against Serie A newcomers Sassuolo.
The 2006 World Cup winner is struggling with an ankle injury.
Cagliari will be bolstered by the return of playmaker Andrea Cossu for their trip to Florence. He has recovered from a muscular injury and is set to make his season debut at Fiorentina on Sunday.
Livorno fans will have to play the waiting game to see new signing Miguel Borja make his Serie A debut.
The Colombian striker has yet to acquire the work permit he needs to play in Italy and will therefore not feature in Sunday's game against Catania.