The 23-year-old midfielder replaced the retired Russell Anderson during the summer and has skippered the Dons to their best start to a league season since the glory years of the 1980s.
McInnes told the club's official website: "With Russell retiring that responsibility had to fall on someone and I feel that Ryan will flourish under the responsibility of that role. I believe it will help his development as a player.
"He is a very influential player for us anyway and we are looking for that influence now as captain.
"It has to be said that when you consider who could have been your captain there were a number of players who came into my thoughts.
"Mark Reynolds will do what he has done for the last few years by supporting Jacko from the position of vice-captain. He is brilliant in that role. There are a few other players there who would make good captains, but only one player can wear the armband."