The present study was carried out to determine the prevalence of subclinical mastitis in cattle in eighteen herds in the center region of Algeria. Milk samples were collected from 560 quarters of 140 cows free of clinical mastitis. The samples were subjected to California Mastitis Test (CMT) and the positive samples were analysed by bacteriological culture and Speed Mam® Color. The overall quarter prevalence was 28.77% whilst animal prevalence was 28.57%.Bacteriological analysis showed that there was a wide range of bacteria that cause these infections. Staphylococcus aureus (40%) was found to be the most prevalent organism followed by Streptococcus spp. (12.5%), Enterobacteriaceae (2.5%), Pseudomonas spp. (2.5%), Staphylococcusaureus + Streptococcus spp. (12.5%), Streptococcus spp.+ Escherichia coli (7.5%), S. aureus + Mycoplasma spp.(7.5%), and S. aureus +Streptococcus spp.+ E. coli (5%).