Equine endometritis is one of the most common causes of reproduction failure. To achieve better treatment outcomes, different diagnostic methods should be combined. In the current study, 39 repeat breeder mares were subjected to ultrasonography examination to detect excessive accumulation of intrauterine fluids and an abnormal oedema pattern, which revealed that 61.5% of mares were positive. Combined with endometrial cytology by low-volume uterine flush, 47.7% of smears contain neutrophils (more than 2-3 per HPF X100), and microbial culture. 92.3% of mares were infected with different bacterial isolates, such as Escherichia coli, Streptococci, Staphylococcus, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter freundii, Providencia alcalifaciens, and Proteus mirabilis. All mares were given saline solution and gravity withdrawal before being given 20 IU of oxytocin (as ecbolic agents). Mares were divided into three groups; Group one (n=15) received an intrauterine infusion of 20 mL of freshly prepared autologous platelet-rich plasma (PRP) 6 h after breeding, Group two (n=15) was treated with three doses of systemic Enrofloxacin 5% during the estrus period, and Group three (n=9) received only uterine lavage and 20 IU of oxytocin. PRP and Enrofloxacin resulted in a significant (p < .05) reduction in endometrial thickness (oedema; 5.05 and 6.74 mm, respectively) and disappearance of intrauterine fluids compared to the control (10.98 mm). Furthermore, PRP (days) and Enrofloxacin (17.89 days) reduced the days to the next oestrus compared to the control (18.58 and 17.89 vs. 21.19 days, respectively). Furthermore, the pregnancy rate improved to reach 70% in the PRP group and 60% in the Enrofloxacin group, while the control remained low at 22%. In conclusion, autologous PRP can be used as a low-cost alternative therapy for modulating the inflammatory process and effectively treating mares' endometritis.