Particle electrification is an inevitable phenomenon in various powder handling processes. Here the contact electrification of particles is discussed and it is revealed that the physical properties as well as the contact potential difference between a particle and the wall have an important role in the particle electrification. In actual processes, particle concentration and equipment size can also affect the electrification. Additional important factors are time constants of charge generation and charge relaxation relating to the contact frequency between particle and wall. Further, a contact potential measuring system developed in our laboratory is discussed showing the effectiveness in the evaluation of functional composite particles.