The level of nitric oxide (NO) is important to protect the heart from ischemic damage in acute coronary syndrome (ACS) patients. S-nitrosothiol (SNO) is a molecule that represents the main form of NO storage in the vascular structure. In addition, dynamic thiol/disulfide homeostasis (TDH) is known to play an important role in maintaining the oxidant-antioxidant balance. In this study, our aim is to evaluate the oxidative/nitrosative stress status according to SNO level and TDH in patients with ACS. The study included 124 patients who were admitted to the emergency service and 124 consecutive individuals who applied to the cardiology outpatient clinic with cardiac complaints and underwent coronary angiography (CAG). Blood was drawn from all participants included in the study to determine SNO, nitrite, total thiol, native thiol, and disulfide levels after 12 h of fasting. Serum SNO levels were found to be significantly lower in ACS patients compared to the control group (0.3 ± 0.08 vs. 0.4 ± 0.10 μmol/L, successively, p < 0.001). In addition, while the total thiol, native thiol, and native thiol/total thiol levels were lower in the patient group compared to the control group, nitrite, disulfide/native thiol and disulfide/total thiol levels were higher. As a result of multivariate logistic regression analysis, it was determined that age, gender, smoking, low-density lipoprotein cholesterol, glycosylated haemoglobin, and SNO levels were independent predictors in predicting ACS patients. S-nitrosothiol and thiol levels were found to be significantly lower in ACS patients. In addition, SNO molecule was independently associated with the presence of ACS diagnosis.