Casizolu is a traditional Sardinian (Italy) pasta filata cheese made with cow raw milk belonging to Sardo-Modicana and/or Bruno-Sarda breeds added with natural whey starter. This work aims to describe the traditional technology of this product and to evaluate the microbial groups/species involved in the first month of ripening.Raw milk, curd after stretching and Casizolu cheese samples from two different farmsteads were subjected to enumeration of microbial groups, isolation and genotypic characterization of isolates and PCR temporal temperature gel electrophoresis (TTGE) analysis. The counts of lactobacilli and lactococci groups in raw milk were about 5-6 log UFC ml(-1) of milk. These counts tended to increase in curd and cheeses, reaching values higher than 8 log UFC g(-1) of cheese. Culture dependent and independent approaches employed in this work highlighted the fundamental role of Lactococcus lactis subsp. lactis, Streptococcus thermophilus and Lactobacillus paracasei in the manufacture and ripening of Casizolu cheese. Other species frequently isolated were Enterococcus durans, Enterococcus faecium, Enterococcus italicus while Enterococcus lactis, Streptococcus parauberis, Lactobacillus plantarum, Lactobacillus pentosus, Lactobacillus brevis, Lactobacillus fermentum and Lactococcus raffinolactis were isolated occasionally.Lactococcus lactis subsp. lactis, Strep. thermophilus and Lact. paracasei were the principal bacterial species involved in the Casizolu cheese manufacturing and ripening. For the first time, Ent. italicus and Ent. lactis were isolated in the pasta filata cheese.This study shows the first data on microbial groups and species involved in the manufacture of Casizolu cheese and highlights the role of Lact. paracasei and Enterococcus spp. from the earliest stages of ripening cheese; furthermore, provides evidence that raw milk cheese is a source of new strains and therefore a reservoir of microbial biodiversity.