Background: Brain dysfunction is associated with increased mortality in high care unit. Brain dysfunction due to convulsive seizures, nonconvulsive seizures or ischemia, may be difficult to identify by neurological examination. EEG examination can identify brain dysfunction.The aim of this study is to describe the most EEG pattern in critical ill patient with decreased level of consciousness at high care unit Methods: This is a retrospective study. All patients who were treated in the high care unit and underwent an EEG examination in January-December 2019 was conducted in this study. The outcome of this study such as the sociodemographic patient characteristics (like age, sex and history of seizure during treatment in high care unit, past medical history of seizure), etiology diagnosis and EEG pattern. All data were analyzed using SPSS 25. Conclusion:Continous Slow Activity (CSA) was most commonly abnormal EEG features in critical ill patient with decreased level of consciousness at high care unit.