Objective <p>To investigate the prevalence and associated factors of inappropriate sexual behaviour (ISB) in psychogeriatric inpatients in a Chinese psychiatric hospital.</p> Methods <p>A cross-sectional study was conducted from August to October 2021 among 174 psychiatric inpatients aged 60 years and older at a psychiatric hospital in Huzhou, China. ISB was assessed using the St. Andrews Sexual Behaviour Assessment (SASBA), a structured tool that categorizes behaviors into four domains: verbal, non-contact, exposure, and physical contact. Sociodemographic data, clinical characteristics, activities of daily living (ADL), and serum hormone levels (testosterone, estradiol, progesterone) were collected. Binary logistic regression was used to identify factors associated with ISB.</p> Results <p>Among the 178 patients, 54 (30.3%) exhibited inappropriate sexual behavior. The prevalence was higher in male patients (38.2%) than in female patients (19.7%, <i>p</i> = 0.013). Patients exhibiting ISB were younger (67.1 ± 5.4 years, <i>p</i> = 0.028), had a longer length of hospitalization (42.5 (7.9, 79.5) months, <i>p</i> = 0.003), and lower progesterone levels (0.10 (0.10, 0.28) nmol/L, <i>p</i> = 0.012).</p> Conclusion <p>Inappropriate sexual behavior is prevalent among psychogeriatric inpatients. It is associated with factors including gender, age, hospitalization length, and hormonal levels, especially progesterone.</p>