Depression is a debilitating disease, which, in severe cases, can lead to suicide. However, objective and reliable biomarker for the diagnosis of depression is lack. In this preclinical study, we recorded resting local field potentials (LFPs) from chronic unpredictable stress (CUS)-induced depressed (n =20) and control (n = 20) rats and then compared their gamma activities in terms of single-band and cross-frequency coupling patterns. Both theta-gamma coupling and relative power in total gamma band revealed significant abnormalities in gamma rhythm in the right auditory cortex of depressed rats. These findings implied that resting-state gamma rhythms may be a promising objective diagnostic biomarker for depression. Furthermore, our research provided direct evidence from the perspective of source signals in deep brain sites, which might be useful for clinical applications.Clinical Relevance- This research showed that resting gamma in the auditory cortex is a promising biomarker for depression diagnosis.