Dengue is an important public health problem, which caused by the dengue virus (DENV), a single-stranded RNA virus consisted of four serotypes. Central nervus system (CNS) impairment in dengue usually results from DENV-2 or DENV-3 infection, which lead to life-threatening outcomes. Furthermore, neurological complications due to DENV-1 was rare especially in adult patients. A 44-year-old man without comorbidities had lethargy after hyperpyrexia and a positive DENV NS1 antigen was detected for confirming the diagnosis of dengue on day 8 of onset. Then logagnosia, decreased muscle strength, delirium and irritability were occurred even radiographic examination were normal. He was treated with low-dose hormone, sedatives and gamma goblin with a short duration of 6 days. The cerebrospinal fluid (CSF) tests were persistent normal. However, presence of DENV-1 RNA was confirmed both in CSF and serum. Furthermore, the complete sequence of the DENV isolated from the patient's serum was performed (GenBank No.: MW261838). The cytokines as IL-6, IL-10 and sVCAM-1 were increased in critical phase of disease. Finally, the patient was discharged on day 24 of onset without any neurological sequelae. Encephalopathy caused by a direct CNS invasion due to DENV-1 during viremia was described in an adult patient. Treatment with low-dose hormone and gamma goblin was helpful for admission.