The nano- and micro-indentation mechanical parameters of the AISI 316L stainless steel, such as nanohardness (Н_NI), microhardness (H_MI), the Young modulus (E), the indices of plasticity (H/E) and resistance (H³/E²), and relaxation parameters h_s, h_res, h_e-p and their dependences on the value of P load applied to an indenter were studied. Hardness is shown to be slightly decreased in the microindentation interval (Р = 100–500 mN) with an increase in the load, whereas it grows substantially with P decrease in the region of nanoindentation (Р < 100 mN) to exhibit the Indentation Size Effect. The major peculiarities of the deformation process were established resulting from the study of the indenter penetration character. The presence of various mechanisms of the plastic deformation is supported during the indentation of AISI 316L steel (intragranular, intergranular, and rotational), and a physical interpretation of the observed patterns is offered. The results obtained are of great importance for practice, since the compound AISI 316L belongs to medical steels being used as implants in stomatology, bone impregnation, and biotechnology.