Background: Although studies on the effectiveness of the use of ICU diaries on psychiatric disorders and quality of life have been published, the results still seem to be controversial. The study aimed to determine the effects of using an ICU diary on psychiatric disorders, sleep quality, and quality of life (QoL) in adult ICU survivors in China. Methods: One hundred and twenty-six patients who underwent a scheduled cardiac surgery and were expected to stay ≥ 24 h in ICU were randomized to two groups (63 in each group). The patients in the intervention group received the use of ICU diaries during the period of post-ICU follow-up, while the patients in the control group received usual care without ICU diaries. The primary outcome was significant PTSD symptoms (Chinese version of Impact of Event Scale-Revised, IES-R; total score ≥ 35 was defined as significant PTSD symptoms) and its severity in patients 3 months post-ICU. The secondary outcomes included memories of the ICU at 1 month, QoL (Medical Outcomes Study 36-item Short-Form, SF-36), sleep quality (Pittsburgh Sleep Quality Index Questionnaire, PSQI), anxiety, and depression symptoms (Hospital Anxiety and Depression Scale, HADS) at 3 months. Results: Eighty-five and 83 patients completed the follow-up interviews at 1 month and 3 months post-ICU, respectively. Significant PTSD symptoms were reported by 6 of 41 (14.63%) in the intervention group vs 9 of 42 (21.43%) in the control group (risk difference, − 9% [95% CI, − 2% to 21%], P = 0.10). There was no significant differences between groups in IES-R score, symptoms of intrusion, symptoms of avoidance, numbers of memories of feeling and delusional memories, SF-36 score and anxiety score (P > 0.05), while significant differences were found in symptom of hyperarousal score, numbers of factual memories and PSQI score (P < 0.05). No adverse effect was reported. Conclusions: Using an ICU diary is not useful for preventing PTSD symptoms and anxiety symptoms and preserving the quality of life of the patients at 3 months post-ICU, while it significantly improves the survivor's factual memory of ICU and sleep quality, and prevents the hyperarousal symptom.