Objective This study aims to identify the correlation between bispectral index (BIS) value and modified Glasgow Coma Scale (MGCS) score in dogs with altered level of consciousness (ALOC). Design This prospective, observational, clinical study was conducted from February 2016 to March 2017, and follow‐up was conducted until the death of dogs or their discharge from the hospital. Setting This study was performed at the Small Animal Teaching Hospital. Animals A total of 31 client‐owned dogs (males, 20; females, 11) with ALOC and MGCS score <18 with no restrictions for age, breed, sex, and body weight were included. Dogs that received neuromuscular blocking agents before MGCS score evaluation were excluded. Interventions BIS values were measured using the Covidien BIS Loc 2 Channel OEM module and a pediatric 4 sensor with a bifrontal application pattern. Measurements and Main Results Minimal databases of initial neurological assessment, blood profiles, and chest and skull radiographs were developed. In addition, MGCS scores and BIS values were recorded. The mean BIS values for mild, moderate, and severe brain injuries were 89.14 ± 6.52, 77.21 ± 9.82, and 50.58 ± 27.04, respectively. Correlation analysis revealed a significantly positive relationship between BIS values and MGCS scores (r = 0.75; P < 0.001). Conclusions The significant correlation observed between MGCS scores and BIS values in dogs with ALOC demonstrated the usefulness of BIS as an alternative to MGCS for monitoring consciousness in patients with ALOC caused by traumatic brain injury, encephalitis, etc.