The Chelsea manager anticipates his Blues to be joined by Manchester United, Manchester City, Arsenal, Liverpool and Tottenham in the title race.
Last season’s top three - Manchester United, Manchester City and Chelsea - have all changed managers ahead of the new campaign, leaving the league more open than ever.
Those three teams have won the last nine titles between them, but Mourinho, who returned for a second spell in charge at Stamford Bridge in June, feels Arsenal, Liverpool and Tottenham could also be in the mix for top spot come next May.
"I think to start there will be six teams. There is still more than a month for the transfer window to close. It depends on that. In these six teams a lot can happen," Mourinho told The Independent. "Probably many people think Liverpool. Why not? They have a great coach [Brendan Rodgers] and he is there for the second year. He had one year to start with his ideas so why not Liverpool?
"Tottenham - why not? Because they don't have that winning culture of the last years? That's not the point. The point is the squad they have, which is fantastic, and again it's the second season for Andre [Villas-Boas].
"Arsenal is Arsenal and probably they will be a better team. Chelsea is Chelsea. Manchester City and Manchester United, the champions of the last two years.
"Probably by December it will be five or four, but to start I would say all six."