Objective: Post-traumatic stress disorder (PTSD) is a serious mental health challenge that usually lacks effective responses to conventional therapies. High-definition transcranial alternating current stimulation (HD-tACS) is gaining attention as a potential therapeutic approach for neuropsychiatric disorders. This study aimed to investigate the effects of 1-Hz tACS on PTSD symptoms. Methods: A randomized controlled trial involving 40 PTSD patients was designed. Patients were randomly divided into sham and real stimulation groups and underwent 10 HD-tACS sessions. We used 1-Hz HD-tACS with the central anode positioned at T8 and the ring cathodes at P8, C4, F8 and EX10 (targeting right lateral temporal cortex). Clinical symptoms of patients were evaluated through the PTSD Checklist for DSM-5 (PCL-5). Also, we measured salivary cortisol levels and serum brain-derived neurotrophic factor (BDNF) levels before and after treatment. Results: The real stimulation resulted in a more significant reduction in PTSD symptoms as measured by the mean PCL-5 score (56.25 ± 12.13 to 39.40 ± 13.91) compared to the sham stimulation (p ＜ 0.05). The mean salivary cortisol level increased significantly in the real stimulation group (0.053 ± 0.04 μg/dl to 0.10 ± 0.07 μg/dl) compared to the sham (p ＜ 0.001). In contrast, serum BDNF levels showed no significant changes in either group. Conclusion Preliminary findings suggest that HD-tACS in delta band can significantly alleviate PTSD symptoms, indicating its potential as a therapeutic intervention for PTSD.