Milan have announced a six-month deal on this occasion, meaning Beckham will remain in Italy up until the 2010 World Cup finals in South Africa.
AC Milan vice-president Adriano Galliani said on the club's official website, www.acmilan.com: "We are very happy to see again David Beckham with the Rossoneri jersey after the splendid experience of last season."
He added: "We are certain that this time in Europe will help the player take part in the next World Cup and to continue after his career in Los Angeles Galaxy, to whom we thank for their time."
Former England captain Beckham had been strongly linked with a second loan spell with the Rossoneri to improve his chances of making Fabio Capello's World Cup squad.
Galliani claimed last week an announcement was imminent - and it has been confirmed on the club's official website on Monday evening.
Beckham moved to the San Siro during Major League Soccer's off-season last January, initially on a three-month loan deal, but impressed so much his stay was extended until the end of the Serie A campaign.
The 34-year-old returned to the Los Angeles Galaxy in the summer after helping Milan to fourth place in Serie A, with two goals in 18 league appearances.
His first Serie A game this season could be against Genoa at the San Siro on January 6.
A statement from LA Galaxy read: "We have completed the loan agreement of midfielder David Beckham to AC Milan, effective in January. Beckham remains under contract to the Galaxy and will play for the club throughout the MLS Cup play-offs, which continue on Sunday."