The ascending reticular activating system (ARAS) is known to play an essential role in maintaining arousal and consciousness. In this report, we describe the case of a patient with impaired consciousness due to injury of the ARAS after bilateral pontine infarction. A 73-year-old female patient presented with anterior chest pain to the Emergency Department of our university hospital. She was diagnosed with chronic stable angina pectoris, three-vessel disease, and chronic total occlusion of the left anterior descending artery by coronary angiography and received conservative treatment. After five days, she showed deep drowsy mentality and brain MRI revealed bilateral paramedian pontine infarction. Four weeks after the pontine infarction, she showed severely impaired consciousness, with a Glasgow Coma Scale score of 7 (eye-opening: 2, best verbal response: 2, and best motor response: 3). Coma Recovery Scale-Revised score was 10 (auditory function: 2, visual function: 3, motor function: 2, verbal function: 2, communication: 0, and arousal: 1). Results of diffusion tensor tractography (DTT) for the ARAS showed decreased neural connectivity in the left lower dorsal ARAS, both lower ventral ARAS, and both upper ARAS. To the best of our knowledge, this is the first report of injury to the ARAS in bilateral pontine infarction diagnosed by DTT. We presume that our report would provide clinicians a better understanding of the mechanism of impaired consciousness in patients with pontine infarction.