Gastroesophageal reflux disease (GERD) is a common disease with increasing prevalence worldwide. However, the diagnosis of GERD is challenging because there are no definite gold standard criteria. Recently, a novel impedance parameter, namely mean nocturnal baseline impedance (MNBI), has been proposed, which reflects the burden of longitudinal reflux and the integrity of esophageal mucosa. MNBI has shown an immense promise for increasing the diagnostic rate of multichannel intraluminal impedance-pH (MII-pH) monitoring and predicting the response to proton pump inhibitor (PPI) or anti-reflux intervention in patients with reflux symptoms. The present paper reviews the association between baseline impedance and esophageal mucosal integrity, the acquisition of MNBI in 24-h MII-pH monitoring, the clinical utilization of MNBI in improving the diagnosis rate of GERD in patients with typical reflux symptoms, predicting the response to PPI or anti-reflux treatment in these patients, the utilization of MNBI in diagnosing patients with atypical symptoms or extra-esophageal symptoms, and the correlation between reflux burden and MNBI. MNBI should be routinely assessed using MII-pH monitoring.