Observations of micromagnetic dynamics in magneto-optical recording media have been performed using a static tester and a loop tracer. The magnetization reversal, domain structure and annealing treatment of amorphous rare earth-transition metal (RE-TM) alloy fIlms as well as multilayered cobalt-platinum (Co/Pt) thin films have been studied. The magnetization reversal was investigated in both nucleation-dominated and wall-motion-dominated media. The degree of jaggedness of various domain structures has been compared in terms of the fractal dimension of domains. We find that the magnetization reversal processes are intimately related to the jaggedness of domain surface. The fractal dimension increases monotonically from wall-motion-dominated films to nucleation-dominated films. The relationships between the hysteresis loop and the reversal process are also discussed.