In this study, nanostructured diamond (NSD) films were grown, by microwave plasma assisted chemical vapor deposition (MP-CVD) technology, on WC-Co drills for performance enhancement in dry drilling of A390 alloys. Surface cobalt was removed by a well-controlled precision etching process. H2/CH4 gas mixture with a small amount of N2 was applied to produce NSD films. Moreover, slight hone was applied to the cutting edges prior to the NSD deposition to relieve residual stresses generated by thermal mismatch in depositions. The results show feasibility of dry drilling of A390 alloys by NSD coated drills, substantially outperforming carbide drills.