The maturity model developed in the present study, called “P4M: Project Management Maturity Mixed Model”, has a hierarchical character and can be integrated, if necessary, with the OPM3 process-oriented model. This gives it flexibility and adaptability with the different categories of business and standards used. In this research, we take a particular case of implementation of an improvement action according to the cycle of OPM3, namely the implementation of a PMO according to the framework presented in a previous research (H.Tahri, 2013) and taking into account the "P4M" model (H.Tahri2015). This model can be used regularly by the same entity (strategic PMO: EPMO) or an external entity, to evaluate project management maturity in the organization and evaluate the maturity of the operational PMOs if they exist, as well as initiating roadmap for improvement and change through the same model. The approach used to initiate change or improvement actions perfectly matches the OPM3 cycle (acquiring knowledge, conducting evaluation, and managing improvements). The capabilities used in the PM4 evaluation matrix can be enhanced by other capabilities derived from the company's proprietary model or existing standards.