Introduction: The main pulmonary embolism is a blockage of blood flow to the lungs by a blood clot which is composed of clumped platelets and condensed fibrin lodged into an artery in the lungs. A condition associated with thrombotic events due to loss of endothelium non- thrombogenic protective factors and severe dehydration might occur in the early course of severe dengue, thereby increasing the risk of embolic formation. We report acute pulmonary embolism in a severe dengue patient co-infected with influenza B, which might additionally predispose to an acute embolic event. Case description: This 71-year-old diabetic woman with hypertension suffered from the dizziness, episodic fever, and general weakness since September 13, 2015. The data of dengue virus IgM, IgG and NS1 antigen were all positive. The presenting platelet count was 11000/uL. She felt worsening malaise, dizziness, anorexia, and newly developed dyspnea. The brain CT did not indicate obvious lesion except mild atrophy. The chest X-roentgenogram (CXR) revealed the opacity in left lower lung field. Abnormal liver function tests were noted, including S-GOT (AST), 1526 U/ L; S-GPT (ALT), 709 U/L; total bilirubin, 2.71 mg/dL and direct bilirubin, 1.84 mg/dL. Under the impression of severe dengue with pneumonia, she was admitted for the further management. Antibiotic therapy with cefuroxime was given. However, the patient had worsening dyspnea and tachycardia 5 days later. Laboratory data showed elevated lactate (4.1 mmole/L), hypoxemia with mild decrease PaO2/FiO2 ratio, and elevated D-dimer (3271 ng/m). CXR showed resolution of pneumonia patch. As suspected pulmonary embolism, chest CT was arranged, which revealed partial thrombosis of right pulmonary artery at superior lobar branch. Therefore, she was admitted to the intensive care unit. In addition, the result of rapid influenza diagnostic test for influenza B antigen was positive. A 5-day course of oseltamivir and antibiotic therapy with levo- floxacin were given. After treatment, fever subsided and dyspnea was improved. Follow-up platelet count rose to 91000/uL. Then, she was transferred to ward. After heparin therapy, subsequent daily warfarin was titrated to daily 2.5mg to achieve the desired prothrombin time ratio. As stable condition, she was discharged after 16 days of hospitalization. Conclusion: Pulmonary embolism has been reported in association with dengue fever or severe influenza, particularly influenza A(H1N1). Co- existence of severe dengue, influenza B and acute pulmonary embolism was sparsely reported before. Awareness for these complications should be recommended to all practitioners who treat patients with severe dengue fever, particularly co-infected with influenza.