Background: Hypercoagulation in COVID-19 is known to increase the risk of vascular thromboembolism and mortality. Unfractionated Heparin (UFH) is an anticoagulant used to prevent venous thromboembolism. Inadequate dose causes unachieved therapeutic targets, while large dose increases the risk of bleeding. For this reason, the laboratory marker that has most sensitive to detect bleeding tendency is of utmost importance. APTT is a common laboratory test used to therapeutic targets but its sensitivity is still debatable. Thromboelastography (TEG) seems more promising for this purpose in other clinical condition. This study is aimed to compare APTT and Thromboelastography (TEG) in detecting bleeding tendency in critically ill COVID-19 patients treated with heparin. Methods: This study is an analytic observational study in a retrospective design. The method used is total sampling, through several inclusion criteria. Inclusion criteria include: age >18-year-old, confirmed COVID-19 with RT-PCR results, hospitalized in Special Isolation Room, received UFH therapy, and examined for TEG and APTT at the same time. The subjects of this study were divided into two groups, the bleeding and non-bleeding groups. Suitability in APTT between the two groups were analyzed using the Kappa test, suitability in various TEG parameters were analyzed using the Kappa test, and differences APTT and TEG were analyzed using Fisher's exact test. Results: This study showed that there were significant differences in the APTT and had a weak concordance for the incidence of bleeding in these two groups (p: 0,002; k: 0,340); significant differences in various TEG parameters (p < 0,05), namely R time (k: 0,340), K time (k: 1,0), ? angle (k: 0,821), MA (k: 0,701) and CI (k: 1,0), but LY30 no significant difference (p > 0,05). K time and CI had a perfect concordance for the incidence of bleeding. In addition, there was a significant difference in APTT and TEG between the two groups (p: 0.000). Conclusion: TEG shows better description the bleeding condition compared to APTT in critical COVID-19 patients treated with heparin.