Abstract: This study was undertaken to determine aetiology and prevalence of  subclinical mastitis in manually and mechanically milked animals in the north of  Palestine. Milk samples from animals with bacterial infection of the mammary gland  showed significantly higher somatic cell count (SCC) than did the corresponding  milk from healthy animals, which (1,420±100 X103 cells/ml; vs. 330±35 X103  cells/ml; 1650±155 X103 cells/ml vs. 490±40 X103 cells/ml; 520±50 X103 cells/ml  vs. 140±25 X103 cells/ml) for ewes, goats and cows, respectively. The prevalence of  bacterial isolation of the milk from goats (n = 25), sheep (n = 40) and cows (n=220)  from several major herds was determined. Culturing for bacteria revealed that 52 %, 72.5% and 59.1% of tested goats, sheep and cows had subclinical mastitis, respectively. Most pathogens (90.6%) isolated from milk samples were Gram positive bacteria. Staphylococci (68.3%) were the predominant cause of subclinical  mastitis. Coagulase-negative staphylococci and coagulase-positive staphylococci accounted for 35.6% and 32.7% of the total bacteria isolated, respectively. Other mastitis pathogens isolated include Micrococcus spp (18.3%), Proteous mirabilis (9.4%) and Bacillus spp (4.0%). Early diagnosis of subclinical mastitis in dairy animals may be important in reducing production losses and enhancing prospects of recovery herds in order to avoid the development of clinical mastitis.