A function f is self-similar if, modulo an error regular function g, it (i.e., f ) is invariant under specific transformations involving mainly dilations and translations (known as the piecewise linear dynamical systems). The multi-fractal formalism for functions has been proved to be valid for a large class of self-similar functions. For the computation of the spectrum of singularities for such functions, Gibbs measures were constructed. The authors have extended the validity for quasi-self-similar functions of the form (17).