Footage of the scurrying rats will be broadcast from a video tape nestled among festive presents laid at the base of the otherwise cheerful and conventional pine tree.
The tree, an angel on its peak and the rats at its base, was designed by maverick high-tech artist Mat Collishaw, 33. The contrasting images are meant to be thought-provoking rather than in bad taste, the Tate Gallery insisted.
"What Mat does is to juxtapose different images in order to provoke you to think a bit deeper about things," a spokeswoman said. "The juxtaposition of the rats nibbling at mince pies with the rest of the tree tells us that there is another side to Christmas and things may not always be as glittery as they seem.
"This is the twelfth year that we have commissioned a tree and this is the first time for several years that we have had a traditional Christmas Tree in the gallery. I do not think it is an offensive work."
Mr Collishaw was commissioned to design the tree as he is "a young British artist - someone exciting, with good ideas," the spokeswoman said. His work has sparked strong feelings since he was an undergraduate at Goldmiths College, University of London. His 1989 degree show featured back-lit photographs, from criminology textbooks, of murdered women. One of the external examiners refused to mark it.
The spokeswoman added: "We are a gallery for the collection of contemporary art. What Mat is saying with this Christmas tree is very thought-provoking."
The tree and the gallery's 1999 Christmas card are supported by the Patrons of New Art, which was set up in 1982 to help provide financial support towards acquisitions for the gallery's contemporary art collection.