Min Gao,1,2,* Wenhua Sang,1,3,4,* Kun Mi,1,3,4 Jiancong Liu,1,3,4 Yudong Liu,1,3,4 Wenge Zhen,1,3,4 Bang An2 1Department of Affective Disorders II, Hebei Provincial Mental Health Center, Baoding, People’s Republic of China; 2Xianyang Central Hospital, Xianyang Mental Health Center, Xianyang, People’s Republic of China; 3Hebei Key Laboratory of Major Mental and Behavioral Disorders, Baoding, People’s Republic of China; 4The Sixth Clinical Medical College of Hebei University, Baoding, People’s Republic of China*These authors contributed equally to this workCorrespondence: Wenhua Sang, Department of Affective Disorders II, Hebei Provincial Mental Health Center, Hebei Key Laboratory of Major Mental and Behavioral Disorders, The Sixth Clinical Medical College of Hebei University, Baoding, People’s Republic of China, Email whsang997169@163.com Bang An, Xianyang Central Hospital, Xianyang Mental Health Center, Xianyang, People’s Republic of China, Email xyanbang@163.comObjective: Only about one-third of depressed patients respond to initial antidepressant treatment. Therefore, it is crucial to find effective predictors of antidepressants. The purpose of our study was to learn the relationship between EEG theta power, theta asymmetry, and the efficacy of escitalopram.Methods: The study included 34 patients with depression. Before and after each patient’s course of treatment, EEG data was gathered. Both the Hamilton Anxiety Scale (HAMA) and the 17-item Hamilton Depression Scale (HAMD-17) were evaluated simultaneously. The natural logarithm of right frontal theta power minus left frontal theta power was used to calculate inter-electrode theta asymmetry (AT).Results: First, our study found no statistically significant difference between intra-electrode theta power and inter-electrode AT before and after treatment (P ≥ 0.05). When we later looked at the data regarding treatment effects, the findings revealed that patients (n = 9) who did not respond to treatment had lower baseline theta power at C4 [6.190 (2.000, 12.990) vs 15.800 (7.255, 22.330), z = − 2.166, P = 0.030]. The two groups had no difference in other electrodes (P ≥ 0.05). The AT of C3/C4 in non-responders (n = 9) was lower [0.012 (0.795) vs 0.733 (0.539), t = − 3.224, P = 0.005]. However, there was no difference in inter-electrode AT between the two groups in F3/F4 and F7/F8 (P ≥ 0.05). We finally show that the theta power at C4 was negatively correlated with HAMD scores before treatment (r = − 0.346, P = 0.045).Conclusion: Our findings determined that increased theta power and positive asymmetry in the right frontal-central area correlate with favourable escitalopram treatment, providing a basis for finding predictive markers for antidepressants.Keywords: depression, EEG, theta power, theta asymmetry, treatment effect