Epidemiological data suggests that approximately 10-65% of patients with mild to moderate COVID-19 have persistent symptoms already after an acute infection, which may last for six months or more. Previous clinical studies have shown that similar symptoms may also occur in the liver. Russian scientists have studied the phenomenon of hyperammonemia in the acute phase of COVID-19, but the problem of elevated blood ammonia levels in post - COVID syndrome has not been studied before. One possible option for the correction of hyperammonemia is the L-ornithine - L-aspartate (LOLA) preparation. The aim of the study was to investigate the manifestation of hyperammonemia in post - COVID syndrome and the possibility of its correction by using LOLA. Eighty-three patients (mean age 51.71 ± 12.82) with post-COVID syndrome, attention and memory impairment, chronic fatigue, hyperammonemia, 2-fold increase of alanine transaminase (ALT) and aspartate transaminase (AST) levels were included into multicenter, prospective observational study. L-ornithine-L-aspartate (LOLA) was given (3 g 3 times per day orally) for 4 weeks to correct hyperammonemia. Patients were accessed by the number connection test (NCT), fatigue evaluation test, measurement of ammonia and ALT, AST levels at baseline, and after 4 weeks. At week 4 the ammonia level was significantly decreased in 81 patients (97.6%). Time (sec) to complete the NCT was 49,43 ± 15,85 vs 64.67 ± 24.95 at baseline (p<0.001). Before treatment, the majority of patients had stage 1 hepatic encephalopathy (HE) - 50.6% and stage 1-2 (intermediate) HE - 30.1%, stage 2 HE - 10.9%, stage 3 HE - 2.4%. After LOLA treatment, the distribution changed: 41% of patients had no HE, 36.1% had stage 1 of HE, 22.9% had stage 1-2 (intermediate) of HE, and stage 2 and 3 of HE was no longer defined. The mean score in fatigue evaluation test was 46,27 ± 10.0 vs 64,71 ± 19,18 at baseline (p<0.001). ALT and AST levels were 47,83 ± 38,21 units/l vs 95,75 ± 68.99 units/l at baseline and 40,10 ± 35,97 units/l vs 78,51 ± 90,90 units/l at baseline respectively (p<0.001). This study showed that the inclusion of LOLA in a dose of 3 g 3 times a day for 4 weeks was associated with significant improvement in the objective and subjective outcomes in patients with post-COVID syndrome.