Thin diamond films are deposited on commercial tungsten carbide micro ball end mill by using hot filament chemical vapour deposition (HFCVD) technique. Raman spectrum results confirm the high purity of sp3-carbon bond diamond of as-deposited films. The scanning electron microscope (SEM) investigation exhibits continuous fine grained diamond films are uniformly deposited on micro ball end mill. Milling of graphite is chosen to check the cutting performance of fabricated diamond coated micro ball end mill. For the sake of comparison, milling test is also carried out using uncoated micro ball end mill under the same cutting parameters. The milling test results show that the tool life of diamond coated micro ball end mill is about 10 times than that of uncoated one, which may attribute to high hardness, wear resistance, low sticking to graphite of deposited diamond films and strong adhesive strength between them and substrate surfaces.