Background: The causative agent of Chlamydiosis, also called enzootic abortion of sheep, is an obligate intracellular Gram-negative bacterium called Chlamydia abortus. Purpose: The aim of this study is to determine the prevalence of Chlamydiosis and changes in oxidative stress levels in sheep abortions in the Black Sea Region. Method: PCR analysis made from aborted fetuses of 393 sheep from 8 provinces between 2019–2021; Presence of C. abortus detected in 65 aborted fetuses (16.5%). In the study, oxidative stress parameters such as CP, MDA, TOS, TAS and OSI levels were investigated. Result: CP, MDA, TOS, TAS and OSI values were respectively as 6.92 ± 2.29 mg/mL, 28.8 ± 4.79 µmol/g, 14.01 ± 7.25 µmol H2O2 Eq/L, 2.19 ± 0.67 mmol Trolox Eq/L, 6.94 ± 4.31 AU in the control group. In the chlamydia infected group, CP, MDA, TOS, TAS and OSI values were 10.96 ± 6.75 mg/mL, 92.31 ± 73.08 µmol/g, 36.04 ± 28.31 µmol H2O2 Eq/L, 1.91 ± 1.02 mmol Trolox Eq/L, 22.39 ± 19.5 AU was determined. Conclusions: CP, MDA, TOS and OSI levels were found to be significantly higher (P < 0.05) in the C. abortus infected group compared to the control group (P < 0.05). It was determined that the TAS level decreased in the infected group compared to the control group, but there was no statistically significant difference (P > 0.05). As a result, it was determined that C. abortus was found at a substantial rate in small ruminant abortion cases in the Black Sea Region. In addition, it was determined for the first time in Türkiye that the oxidative stress increased in abortions caused by C. abortus and infected small ruminants could not produce enough antioxidants. It is thought that this result may be useful in the diagnosis of C. abortus.