<p>To investigate the knowledge, attitude, and practice (KAP) regarding privacy protection in mobile phone use among psychiatric inpatients. This cross-sectional study recruited patients with mental disorders from Nanjing Brain Hospital between January 2023 and April 2024 using convenience sampling. A self-designed questionnaire was employed to collect general information and evaluate privacy protection-related KAP. KAP scores were classified as scores &gt; 85% of the total were considered good, &lt; 60% were poor, and those in between were moderate. A total of 123 questionnaires were distributed, with 120 valid responses, yielding a response rate of 97.6%. The mean total KAP score was 97.91 ± 22.27 (range 21–165), with subscale scores of 31.96 ± 11.01 (knowledge, range 0–60), 28.58 ± 8.35 (attitude, range 9–45), and 35.06 ± 7.77 (practice, range 12–60). Poor scores were observed in 67 (55.8%) participants for knowledge, 34 (28.3%) for attitude, and 56 (46.7%) for practice, with 69 (57.5%) scoring poorly across all dimensions. Higher total KAP scores were significantly associated with female sex (<i>P</i> &lt; 0.01), older age (<i>P</i> &lt; 0.01), mood disorders (<i>P</i> = 0.04), living with a spouse (<i>P</i> &lt; 0.01), being married or divorced (<i>P</i> &lt; 0.01), higher education (<i>P</i> = 0.01), and moderate-to-high economic status (<i>P</i> = 0.01).Psychiatric inpatients showed poor mobile privacy knowledge, needing targeted educational interventions to improve practices.</p>