Two formulations embedding diclofenac sodium salt into a chitosan hydrogel matrix with different crosslinking degree were prepared by in situ hydrogelation. The formulations were investigated by polarized light microscopy and scanning electron microscopy, and the in vitro drug release was tested in a medium mimicking the physiological environment. The mechanism of the drug release has been assessed by a theoretical model which was developed and it was based on the multifractal theory of motion. The drug release mechanism are described through continuous and non-differentiable curves - multifractal curves.