Reversible Posterior Leukoencephalopathy Syndrome (RPLS) is an uncommon neurological disorder which shows the diffuse edema in white matter of occipital lobe of brain. In this report, we describe a RPLS case with Human Immunodeficiency Virus (HIV) infection, whose lesion was improved with Highly Active Antiretroviral Therapy (HAART). A HIV-infected man, who was diagnosed as a mental deterioration with Central Pontine Myelinolysis (CPM) appearing high intensity pontine lesion in brain Magnetic Resonance Imaging (MRI), improved with HAART. No episode of hyponatremia or hypertension was observed in his clinical course. Evaluation of apparent diffusion coefficient (ADC) mapping in diffusion weight imaging (DWI) was performed in brain MRI at the onset and four months after commencement of HAART. ADC mapping enabled to interpret the pontine lesion as RPLS. HAART improved the mental deterioration within two weeks and the elevated ADC value at the onset was normalized at four-month clinical course.