The costumed man allegedly pinched a number of expensive porterhouse products from Raeward Fresh in Nelson last Friday.
The man, dressed in a cow onesie, entered the store with two other people and stole porterhouse steak from the meat section, APN reported.
The trio left in a red car, although witnesses were unable to catch the registration number of the car.
The store manager said staff were alerted by a customer who spotted the shoplifter in action, the report said.
He added that the bizarrely dressed thief was barely given a second glance before he carried out the crime because the costumes are very common in the town.
"The offender was probably not intending to look like the beef they were stealing," added a police spokesman.