Combine all-purpose flour, whole wheat flour, baking powder, sugar, and salt in bowl. Cut in butter with a knife or pastry blender until mixture resembles coarse crumbs; stir in buttermilk until just moistened.
Turn dough out on a lightly floured surface; knead gently 8 to 10 times. Roll to about 3/4-inch thickness; cut with a 2 1/2-inch biscuit cutter. Place biscuits on an ungreased baking sheet.
Bake in preheated oven until biscuits are lightly browned, 10 to 12 minutes.
