Two Staphylococcus xylosus strains were separately used as starter cultures in Soppressata Molisana, a typical Southern Italy fermented sausage, with the aim to obtain an overview of the role of microbial proteolysis. Microbial counts, pH trends and soluble N (NPN, peptide and total amino acid content) were monitored throughout the ripening (26 days) and at the end of storage (94 days) in pork fat or under vacuum packaging. A lower production of soluble N was observed in the traditional batch and in products inoculated with non-proteolytic Staphylococcus xylosus strain. Moreover, staphylococci growth was less vigorous than that observed in the sample inoculated with the proteolytic strain. The results show that the proteolytic phenomena, ascribable to bacterial activity, can take on a meaningful role when the food matrix has been colonised by strains having powerful proteolytic capacities. In fact, the increasing trend in NPN/NT, small peptides and total free amino acids, shown in batch inoculated with proteolytic Staphylococcus xylosus can be justified by a considerable proteolytic and peptidasic capacity exhibited by the strain added as starter. This work could contribute to define the microbiological role of proteolysis occurring in fermented sausage.