Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x5 inch loaf pan.
In a large bowl, cream together the butter and sugar until light and fluffy. Stir in the eggs one at a time, beating well with each addition, stir in the mashed bananas.
In a large bowl, sift together flour, baking powder, baking soda, salt. Blend the banana mixture into the flour mixture; stirring just to combine. Fold in the nuts.
Bake in preheated oven for 60 minutes, until a toothpick inserted into center of the loaf comes out clean.