Annealing processes are an important area of fundamental research within the field of diamond electronic applications. In this study, annealing was applied to as-grown boron-doped diamond films. The current-voltage (I-V) characteristics of the Al/boron-doped diamond films were also investigated. First, the conductivity of films was examined to determine the effect of annealing on boron-doped diamond films. Experimental results indicated that the activation energy for the as-deposited diamond films (intrinsic or light boron-doped) is about 0.38 eV. After annealing, the activation energy did not change. However, the activation energy of the heavily doped films remarkably would change to 0.014 eV after annealing. Next, Fourier transform infrared spectroscopy (FTIR) and cathodoluminescence (CL) were performed to understand more clearly the correlation between the activation energy and the annealing effect on B-doped diamond films. These results revealed that for the lightly B-doped films, the boron atoms were effectively activated at the substitutional site. For the heavily doped case, boron was initially located in an inactive site (e.g., grain boundary, interstitial or clustering sites) and would diffuse into the substitutional site after 900 degrees C annealing.