Background: Nowadays immune checkpoint inhibitors have been used as a therapy in malignant tumor. Immune checkpoint inhibitors can cause various autoimmune side effects. Encephalitis associated with Atezolizumab has been rarely reported as an immune related effect. Case Description: A 56 years old man with lung cancer that has been previously treated with surgery and chemotherapy was admitted with high fever, consciousness disorder, and motor aphasia. MRI report had shown no abnormalities. CSF shown cell count 20/l, protein 166 mg/dl, glucose 73mg/dl, and interleukin 6 82.9 pg/ml. It is diagnosed as Atezolizumab induced encephalitis. Conclusion: Clinicians should be aware of the possibility of encephalitis after initiation of immune checkpoint inhibitors, because these types of case are very few, further investigation will be required to provide effective management for such life threatening conditions.