The two customers ate some of the Organic Marketside Spring Mix salad before the bat was found, officials said. They have been tested for rabies.
The company said customers who may have already purchased the pre-packaged greens, which are sold mainly in southern states, should discard them.
Walmart also said customers can request a full refund for the product.
The two people began eating the salad before they discovered the bat, which was found in a "deteriorated condition", according to the Centers for Disease Control and Prevention (CDC).
The bat was sent to a CDC lab and tested for rabies.
"Both people report being in good health and neither has any signs of rabies," the CDC said in a statement.
The agency also advised anyone who may have already eaten one of the affected salads and found "animal material" to contact their local health department immediately.
But people "who have eaten the recalled salad and did not find animal material are not at risk and do not need to contact their health department", the CDC added.
The salads, which bear the production code G089B19, are exclusively sold at Walmart stores throughout the southeastern US.
The company said it worked quickly with officials to remove the entire batch of salads from store shelves, and only one line of its products had been affected.
"Fresh Express takes matters of food safety very seriously and rigorously complies with all food safety regulations including the proscribed Good Agricultural Practices," a company statement said.
Walmart has issued a recall on a packaged salad after Florida customers found a decomposing bat inside the box.