Preheat the oven to 350 degrees F (175 degrees C). Generously grease a 9×13 inch baking pan.
In a large bowl, mix together the spice cake mix and canned pumpkin until well blended. Spread evenly into the prepared pan.
Bake for 25 to 30 minutes in the preheated oven, or until a knife inserted into the center comes out clean. Cool and serve, or store in the refrigerator. This tastes even better the next day.