The present study aimed to diagnose mare endometritis using ultrasonography, microbial isolation and identification, in addition to blood biochemical characteristics. The study was carried out on a total of 22 Arabian mares divided into 2 groups: normal uterus (n=5) and endometritis (n=17) groups. Depending on age, mares were classified into 2 groups (≤ 10 years and > 10 years). Mares were subjected to ultrasonographic examination to determine uterine wall thickness, edema, and echogenicity. Endometrial samples (swabs) were collected and cultured for microbial isolation and identification. Blood samples were collected, and serum was separated and analyzed to determine the levels of total antioxidant capacity (TAC), nitric oxide (NO), malondialdehyde (MDA), and interleukin-6 (IL-6). The results revealed an increased incidence of endometritis (P < 0.05) in older mares (> 10 years, 85.7%) compared to young ones (≤ 10 years, 37.5%). Endometritis increased the uterine wall thickness, uterine wall echogenicity, and intrauterine fluid (P