<p>The aim of this study was to evaluate serum Testican-1 levels in the diagnosis of clinical and subclinical mastitis in sheep. The animal material of the study consisted of a total of 60 Awassi sheep. The sheep were divided into three groups according to clinical examination findings, somatic cell count (SCC), California Mastitis Test (CMT) results, and bacteriological isolation and identification findings: group 1 (<i>n </i>= 20) consisted of healthy sheep, group 2 (<i>n </i>= 20) consisted of sheep with subclinical mastitis, and group 3 (<i>n </i>= 20) consisted of sheep with clinical mastitis. Blood samples were taken from the jugular vein and centrifuged to obtain serum. Serum C-reactive protein (CRP), serum amyloid A (SAA), and Testican-1 levels were determined in the serum samples using commercial ELISA kits. The obtained data were evaluated using one-way analysis of variance (ANOVA). Statistically significant differences were found between the groups in terms of body temperature, heart rate, respiratory rate, white blood cell (WBC) count, somatic cell count, CRP, SAA, and Testican-1 levels (<i>P </i>&lt; 0.001). In the mastitis groups (clinical and subclinical), all of these parameters were found to be higher than in the control group (<i>P </i>&lt; 0.001). In addition, significant and strong positive correlations were found between Testican-1 levels and body temperature, heart rate, respiratory rate, WBC, CRP, SAA, and somatic cell count (<i>P </i>&lt; 0.01). In conclusion, these findings suggest that Testican-1 can be used as a potential biomarker in the diagnosis of mastitis in sheep.</p>