Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 10 inch Bundt pan.
In a large bowl, stir together the cake mix and instant pudding mix. Add the eggs, sour cream and oil, mix until well blended. In a small bowl combine the sugar, cinnamon and walnuts.
Pour half of the batter into the prepared pan, then place a layer of sliced apples over the batter and sprinkle with half of the cinnamon walnut mixture. Pour the remaining batter over the top and repeat with the remaining apples and cinnamon walnut mixture.
Bake for 60 to 70 minutes in the preheated oven. Cool for 1/2 hour before removing from pan to cool completely.