We have deposited nano-crystalline diamond films in a routine hot filament chemical vapor deposition system,using CH4/H2 gas mixture. We used various measurements such as field emission scanning electron microscopy,micro-Ramnan spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy for characterization. The result show that the films consist of a crystalline diamond phase with small grain sizes ranging rom 20 to 100nm.