Because of the rapid spreading and high mortality of Covid-19, it represents a global problem. According to the literature, an increase in the level of D-dimer was indicated during complications of disease and mortality. To the above-mentioned, we studied the D-dimer level in patients with Covid-19. In total, we investigated 40 Covid infected patients. As research material, we used blood. The research results showed that the level of D-dimer increases significantly in Covid-19 infected patients. And, its increasing level is associated with the severity of patients (p<0,0001). In particular, a high level of D-dimer was shown in the patients that died in the hospital. Therefore D-dimer could be used as a biomarker during Covid disease in Covid-19 patients and for prognosis and treatment management in clinical practice.