Abstract Background Constipation has a high prevalence rate (>30 %) in psychiatric patients with psychotropic drugs. Common pharmacological and non-pharmacological interventions for constipation might have longer-term negative and adverse effects that would outweigh their short-term efficacy in symptom reduction. This randomized controlled trial aims to investigate the effect of self-administered acupressure for the management of constipation, in hospitalized psychiatric patients. Methods Seventy-eight patients were recruited in matched pairs in terms of gender, age and laxative use from five acute psychiatric wards in Hong Kong. Each of these matched pairs of patients was randomly assigned to either a self-administered acupressure (n = 39) or a sham group (n = 39), using computer-generated random numbers. After baseline measurement, the intervention and sham group received the same training in self-administered acupressure and supervised practice once per day for 10 days, except light pressure on non-acupoints was taught to the sham group. The acupoints chosen for acupressure included Zhongwan (RN12), right and left Tianshu (ST25), right and left Quchi (LI11). Participants’ symptoms and quality of life regarding constipation were measured at baseline and immediately and 2 weeks after completion of the interventions with constipation assessment scale and patient assessment of constipation quality of life questionnaire, respectively. Results After 2 weeks follow-up, participants who had received self-administered acupressure indicated significantly greater improvements in both symptom severity (P = 0.0003) and quality of life (P = 0.0004) when compared with the sham group. Conclusion The psychiatric patients with constipation who practiced self-administered acupressure for 10 days improved their symptom severity and perceived quality of life immediately and 2 weeks after completion of the intervention in comparison with the sham group. Trial registration: The trial was registered with the ClinicalTrials.gov (Reg. No: NCT02187640)