The move is seen as a further step to bail out U.S. financial institutions embroiled in wide-spread economic turmoil.
Under an agreement with Morgan Stanley, MUFG will implement a 3billion-dollar portion of the investment via a common share purchase and the remaining 6 billion dollars through the purchase of perpetual preferred shares.
The deal allows MUFG to keep its equity stake in Morgan Stanley above the 20 percent line.
In addition, it will have the right to send and keep an MUFG banker on the Morgan Stanley board as long as it holds a stake of 10 percent or more, Kyodo said.
Mitsubishi, Japan's largest banking group, announced on Sept. 22 that the two firms had reached an agreement on Mitsubishi's purchasing between 10 to 20 percent of the common shares in Morgan Stanley.