Abstract: Among the eight solar system planets, Jupiter and Saturn are the two most giant planets, which also have the most prominent magnetic moments. Comparing to the Earth dipole magnetic field, the magnetic moment of Saturn is about 600 times larger while Jupiter is about 20 000 times larger. The extremely large magnetic moments of giant planets sustain giant planetary magnetospheres, trapping energetic particles with constant electromagnetic perturbations. In this article, we will review the basic pictures of mass and energy circulations in giant planetary space environments, energetic plasma processes in radiation belt, magnetosphere-ionosphere coupling processes and fundamental plasma processes in magnetospheres.