Perturbation of operators is a very rich branch of the modern analysis. The perturbation of Laplacian with inverse square potential arises, in particular, in the studies of non linear Schrödinger equation. So, in this talk, we want to give an explicit and easy characterization of the domain of the operator A=-Δ+b/|x|2. Such characterization is also usefull to determine the domain of A square in a similar way. The study of these operators gives to us a new proof of weighted perturbed Rellich inequalities. This talk is based on a joint work with V. Georgiev and H. Kubo.