Duo presented with gongs on Friday
Mancini won the award for the first time in his career after guiding City to four wins from five matches during the month which put them firmly in the Premier League title race.
City won four of their five matches in December, and completed the year with a 4-0 home win over Aston Villa that sees the club sitting in second place in the table behind rivals Manchester United.
Samir Nasri, meanwhile, impressed once again over the festive period with an eventful month for Arsenal as the club continue to mount a title challenge.
The French midfielder was given the award in recognition of his superb performances during the month, including scoring two goals against Fulham and helping his side to victory over champions Chelsea.
Toast of the City | Mancini is presented with Manager of the Month Award for December