The problem of subclinical mastitis and the associated bacteriological, cytological, and hematological changes were studied in a sheep flock consists of 28 lactating ewes. 56 milk and 28 duplicate blood samples were collected. The milk samples were tested firstly by California mastitis test (CMT) and the animal prevalence rate was 85.7% (24/28) while the udder halves prevalence rate was 67.9% (38/56). By bacteriological examination, Coagulase Negative Staphylococci (CNS) were isolated from 37 samples (as a single pathogen from 33 samples and mixed with Staph aureus from 4 samples) with a prevalence rate 66.1%, while Staph aureus was isolated from 5 samples with a prevalence rate 8.9% (as a single pathogen from 1 sample and as mixed infection with CNS from 4 samples). The isolated bacteria were subjected to the antibiotic sensitivity test and it was found that all the CNS isolates were 100% sensitive to both Enrofloxacin and Gentamicin, while the Staph aureus isolates were sensitive to Enrofloxacin and Oxytetracycline. Somatic cell count (SCC) were estimated in these milk samples and 7 samples were found to have SCC in the range from 250x10³-500x10³ cells/ml and the rest of samples contain SCC level above 500x10³ cells/ml. The results of hematological and serum biochemical examinations revealed that there is no significant changes in the examined parameters between infected or control groups.