The need for safe and effective treatment is becoming increasingly urgent due to the high COVID-19 mortality rates observed worldwide. The choice of drug products for COVID-19 treatment regimens is based on the efficacy and safety data, the mechanism of action, and potential interactions. N-acetylcysteine's (NAC) pharmacological activity and its potential to suppress the progression of COVID-19 make it a promising therapeutic agent for COVID-19. Aim of the study was to evaluate the efficacy of NAC in the complex treatment of moderate COVID-associated pneumonia. Methods. The study included adult patients (n = 46) with moderate COVID-associated (the 2 degree on CT) pneumonia (age 57 (51; 71) years, body mass index – 30 (27.1; 32.3) kg/m , duration of the disease before hospitalization – 7 (6; 8) days, body temperature at the admission – 37.5 (37.1; 37.8)°С). The patients were randomized into two study groups. The 1 group (n = 22) received standard COVID-19 treatment [1]. The 2 group (n = 24) additionally received NAC 1,200 – 1,500 mg/day intravenously. Treatment with NAC was started together with the standard therapy. Results. Our study showed that the inclusion of NAC in the complex treatment of moderate COVID-associated pneumonia led to a statistically significant increase in blood oxygen saturation, oxygenation index, the difference in delta increase in oxygenation index, a quicker reduction in the volume of lung damage, and the difference between the groups in delta reduction of this index. Also, the rate of reduction of C-reactive protein and reduction of the duration of hospitalization in the group of patients who received NAC was statistically significantly more profound than in the standard treatment group. Conclusion. The study confirmed the effectiveness of NAC as a part of the complex treatment of moderate COVID-associated pneumonia. nd 2 st nd