Mancini has been under scrutiny following Manchester City's failure to make it out of their Champions League group and their inability to keep pace with Premier League leaders Manchester United, who enjoy a 12-point advantage.
The Italian's future at Etihad Stadium has often been a matter for debate - particularly when Pep Guardiola's future was undecided - but Mancini says he has been the most successful manager working in England since the end of the 2010-11 season.
In that campaign he won the FA Cup and then added the Premier League title last season thanks to a dramatic 3-2 win over QPR on the final day of the season.
"In the last 15 months I am the best manager in England," Mancini said.
"Someone says for six months that Manchester City would change manager, Guardiola would come in, and after Guardiola went to Bayern Munich, now another manager.
"I won one Premier League, one FA Cup, one charity shield, there is not another manager that's won like me in the last 15 months.
"I can do nothing but it is the reality."
His fellow Italian Roberto Di Matteo might have something to say about Mancini's claim though, having won both the FA Cup and the Champions League with Chelsea last summer before being sacked earlier this season.