The surfaces of Al6061, machined by 150 μm two flute micro end-mills, were studied to determine their roughness. The surface roughness, Ra, was less than 100 nm but the Ra/Rz ratio ranged from 0.03–0.12. The surface roughness was found to improve with increasing width of cut and to a lesser extent with increasing feed rate. A single pass of the end-mill was found to produce a smoother surface than two passes over the same surface. The surface roughness was found to correspond to the diameter of the end mill and the slope of the secondary cutting edge. To reduce the surface roughness, smaller diameter end mills and chip loads should be used.