The interfaces between diamond and metal (Al or Ag) in the diamond/50 vol%Al and diamond/50 vol%Ag composites were characterized by Raman scattering spectroscopy. In the diamond/50 vol%Al composite, graphitization of diamond has been partly detected in the diamond region close to the interface between diamond and Al. On the other hand, a fairly thick graphitized layer of about 8 μm has been formed in the diamond/50 vol%Ag composite. It is concluded that the thick graphitized layer is attributed to the higher sintering temperature in the diamond/50 vol%Ag composite.