Background: After the outbreak of a novel coronavirus (i.e. SARS COV2) in China and its diffusion around the world, great attentions was reserved to the increased incidence of venous thromboembolism in these patients. A specific antiviral action of heparins toward SARS COV2 has been reported in vitro such as a well know action of heparins to prevent VTE in inpatients with infective disease has already been reported since several years. Yet, because fondaparinux represent the pharmacological antithrombotic active sequence of all heparins and because its clinical indication o prevent VTE in inpatients is similar to heprains, we realized a retrospective analysis in inpatients with SARS COV2 on the incidence of VTE during pharmacological prophylaxis with enoxaparin or fondaparinux. This retrospective analysis was named FONDENOXAVID. Methods: We conducted a retrospective cohort study that used patients with SARS COV2 during the Italian outbreak from February 18, 2020 to April 30, 2020. Our aim was to compare the clinical characteristics, prophylactic treatment and outcomes in inpatients positive to SARS COV2 at risk to develop venous thromboembolism, in particular venous thrombosis with or without pulmonary embolism, during in-hospital primary thromboprophylaxis with enoxaparin (40 mg or 60 mg once daily) or fondaparinux (2.5 mg once daily). Statistical analysis was conducted with using MatLab R2016B and eventually ad hoc functions. Results: There were not significative differences in clinical characteristics between patients that used enoxaparin or fondaparinux as thromboprpophylaxis for SARS COV2. The cumulative incidence of thrombotic events was not different in patients that used enoxaparin or fondaparinux as thromboprpophylaxis. No differences were found also in d-dimer and fibrinogen levels test at the admission and after 3 weeks as markers of prolonged inflammation due to SARS COV2. Discussion: The increased incidence of VTE in vivo has been reported in several studies although prophylaxis with low molecular weight heparin was conducted in some of them. The clinical indication to prevent VTE was similar for heparins and fondaparinux. In our results a non-inferiority to prevent VTE was recorded when inpatients with SARS COV2 were treated with prophylactic doses of enoxaparin or fondaparinux according to international guidelines. The incidence of VTE in this retrospective analysis showed that Fondaparinux at fixed doses of 2.5 mg daily was not inferior to enoxaparin (4000 UI daily). Our results testify that fondaparinux and enoxaparin showed the same efficacy to reduce the incidence of VTE in inpatients with SARS COV2.