Sherry Pierce (played by Nia Long), on the run and in hiding from her ex-con ex-boyfriend, knows she can always count on "Big Momma" Hattie Mae Pierce (played by Ella Mitchell). So, when her situation suddenly turns from bad to worse, she decides to go for an impromptu visit. Unbeknownst to her, the FBI is also counting on her showing up at Big Momma's house. Two FBI agents move in across the street and put the house under surveillance. Hilarity begins as these two outsiders try to fit in to small town Southern culture when they so do not blend.
As fate would have it, Big Momma, a midwife by profession, gets an emergency call and leaves town just before the incoming phone call from Sherry. Big Momma is the only connection they have to Sherry and Sherry is the only lead they have on a large pile of stolen money and the man who took it, her ex-boyfriend Lester Vesco. Watching his only lead on a big case dissipate before his very eyes, FBI agent and master of disguise Malcom Turner (played by Martin Lawrence) decides very spur of the moment to intercept the call. Imitating the voice of Hattie Mae, he assures Sherry she is always welcome at Big Momma's.
Much to his partner's dismay, in an instant, his plans to become Big Momma for a week and try to get more information out of Sherry are hatched. Thus is born the plot for a rip roaring comedy-adventure. Malcolm finds himself cooking, delivering babies and proving that grandma's can jump. As if things aren't complicated enough, he also finds himself falling in love with Sherry and wondering whether she really is in cahoots with the criminal boyfriend or just another one of his unfortunate victims.
Will Malcom get his man? Will he also get the girl? Watch this hysterical movie to find out.