The Italian, who signed a new five-year contract during the close season, thinks defending the Premier League crown will be tougher than winning it.
"It is important [to get players quickly] because, after what we did last year, we must continue to win," Mancini said ahead of today's high-profile friendly against Arsenal in Beijing.
"This year will be harder than last so we need to improve our team. We have a man who works for this [the football administrator Brian Marwood] and we hope he can do a good job."
In terms of transfer targets, Mancini has previously expressed his admiration for Robin van Persie and it was confirmed last week City were among the clubs to have lodged bids for last season's Premier League top scorer.
However, Manchester United appear to be favourites to land the Dutchman, and Mancini highlighted the fact that City already have a strong striking contingent.
"Van Persie is an Arsenal player, not our player," Mancini said.
"He is a fantastic player, but we have four strikers and with those strikers we won the title last year.
"Van Persie is a fantastic player, but he is an Arsenal player."
The good news for City is that Vincent Kompany, the captain, has committed his future to the club by signing a six-year contract and the Belgian defender has set his sights on winning more trophies.
"We have laid the foundations and now we want to win more," the Belgium defender told www.mcfc.co.uk.
"If we do that then we can be one of the most successful clubs for a long time to come. That is the aim."
Given the vast changes that have taken place since Sheikh Mansour bin Zayed completed his buyout in 2008, Kompany finds himself as one of the longest-serving members of Mancini's squad.
"I have been here since the beginning and I have seen everything at the club change inside and out," he said.
"This Manchester City project was probably one of the most difficult in Europe and so far we have all done a good job even though a lot of people said it [success] wasn't going to happen so quickly.
"It is good to know that I can be at City for another six years. It is a compliment that the club feels so highly of me.
"Hopefully in the future I will have a bigger impact. My family is happy and there are so many more trophies to win at this club that is why it makes it so special."
"Now is the time to build the culture of winning. We are in the right time; we are in the right moment."
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