ObjectivesTo develop the Psychiatric Nurse Self-Efficacy Scales, and to examine their reliability and validity.DesignWe developed the Improved Self-Efficacy Scale (ISES) and Decreased Self-Efficacy Scale (DSES) using existing evidence. Statistical analysis was conducted on the data to test reliability and validity.SettingThe study’s setting was psychiatric facilities in three prefectures in Japan.ParticipantsData from 514 valid responses were extracted of the 786 responses by psychiatric nurses.Outcome measuresThe study measured the reliability and validity of the scales.ResultsThe ISES has two factors (‘Positive changes in the patient’ and ‘Prospect of continuing in psychiatric nursing’) and the DSES has three (‘Devaluation of own role as a psychiatric nurse’, ‘Decrease in nursing ability due to overload’ and ‘Difficulty in seeing any results in psychiatric nursing’). With regard to scale reliability, the Cronbach’s alpha coefficient was 0.634–0.845. With regard to scale validity, as the factorial validity of the ISES and DSES, for the ISES, χ²/df (110.625/37) ratio=2.990 (p<0.001), goodness-of-fit index (GFI)=0.962, adjusted GFI (AGFI)=0.932, comparative fit index (CFI)=0.967 and root mean square error of approximation (RMSEA)=0.062; for the DSES, χ²/df (101.982/37) ratio=2.756 (p<0.001), GFI=0.966, AGFI=0.940, CFI=0.943, RMSEA=0.059 and Akaike Information Criterion=159.982. The concurrent validity of the General Self-Efficacy Scale was r=0.149–0.446 (p<0.01) for ISES and r=−0.154 to −0.462 (p<0.01) for DSES, and the concurrent validity of the Stress Reaction Scale was r=−0.128 to 0.168 for ISES, r=0.214–0.398 for DSES (p<0.01).Statistical analyses showed the scales to be reliable and valid measures.ConclusionsThe ISES and DSES can accurately assess psychiatric nurses’ self-efficacy. Using these scales, it is possible to formulate programmes for improving psychiatric nurses’ feelings of self-efficacy.