Although several guidelines indicate that daily pharmacotherapy is an important part of the treatment of schizophrenia and major depressive disorder, there are few reports regarding pro re nata (PRN) prescriptions. The purpose of this study is to clarify the characteristics of patients receiving psychotropic PRN prescription for the treatment of schizophrenia and major depressive disorder. We used data from 'the effectiveness of guideline for dissemination and education in psychiatric treatment' (EGUIDE) project to evaluate the presence or absence of psychotropic PRN prescription at the time of discharge, the age and sex of patients receiving PRN prescription for each diagnosis, and the association between PRN prescription and regular daily psychotropics. The psychotropic PRN prescription ratio was 29.9% among 2617 patients with schizophrenia and 31.1% among 1248 patients with major depressive disorder at discharge. In schizophrenia, the psychotropic PRN prescription ratio was 21.6% for patients aged 65 years or older, which was lower than that of all other age groups. In major depressive disorder, the psychotropic PRN prescription ratio was 34.2% for female patients, which was significantly higher than that for male patients (25.5%). In schizophrenia, there was an association between psychotropic PRN prescription and regular use of multiple psychotropic medications. Psychotropic PRN prescription was less common in elderly patients with schizophrenia and more common in female patients with major depressive disorder. In schizophrenia, psychotropic PRN prescription led to polypharmacy of psychotropics. Further studies are needed to accumulate evidence and to provide education on appropriate PRN prescriptions.