Chalk up another win for activist investors, CNBC's Jim Cramer said Monday.
Walgreen will welcome hedge funder Barry Rosenstein to its board of directors. The Jana Partners founder will get a say in choosing at least one additional director, too.
Read MoreWalgreen board adds activist investor
"This is another triumph of activism. I think Greg Wasson, the CEO, is doing a good job, but obviously people have lost faith in him," Cramer said on "Squawk on the Street."
Walgreen, the biggest U.S. drugstore chain, has struggled after lowering its earnings forecast as it completes its merger with Alliance Boots, which runs the United Kingdom's largest drugstore chain.
"I think the combination with Alliance Boots is just beautiful," Cramer said. "My charitable trust has been buying this stock. I didn't expect this. I thought this was an amazing win for the activists."
Jana currently owns roughly 12.5 million shares, about a 1.3 percent stake, in Walgreen, including call options.
—By CNBC's Drew Sandholm.
DISCLOSURE: When this story was published, Cramer's charitable trust owned Walgreen.