Thin diamond films were deposited on different substrates at temperatures below 500 °C by a microwave plasma‐enhanced chemical vapor deposition system. The deposited films were amorphous carbon or diamond films depending on the different gas mixtures used. The addition of oxygen to the gas mixtures was found to be critical for diamond growth at low temperatures. Without oxygen, the deposited films were white soots and easily scratched off. Increasing the oxygen input improved the quality of the Raman peaks and increased the film transparency. The diamond films were also characterized by scanning electron microscopy.