The 19-year-old striker made 14 appearances for the Dons last season during two short spells with the League One club, scoring four goals - including his first professional goal in a 2-1 defeat at Crewe in March.
Bamford's third stint at stadium:mk will last until January 5, 2014 and Dons boss Karl Robinson revealed the youngster was his "number one target" this summer.
"I am very excited by Patrick coming in," Robinson told the club's official website. "I am looking forward to Patrick coming back and wearing our shirt because, to me, he is as good as a young player you are going to get up and down the country.
"Patrick was my number one target and you don't always get your number one target. He is the one I have been waiting for all summer. I could have brought players in over that time.
"It's a risk to put all of your eggs in one basket but on this occasion it was worth the gamble. Thankfully we got the deal done and we're extremely fortunate to have his services for the next few months.
"When I watch Patrick play I see him do things which other players find very hard to do. He is still very young but he is a tremendous talent and when you work with him every day in training you see what quality he possesses."