Introduction Antimicrobial resistance is an infectious disease threat to public health globally, and antimicrobial stewardship among healthcare professionals is one key way to address this potential problem. Registered nurse designated prescribers are the newest group of health professionals to gain prescribing authority in Aotearoa New Zealand, yet little is known about their understanding of their antimicrobial stewardship role. Aim The aim of this study was to explore registered nurse designated prescribers' understanding of their antimicrobial stewardship role through their prescribing practices and approaches to clinical reasoning. Methods This exploratory descriptive qualitative study used individual semi-structured interviews with six registered nurse designated prescribers. Thematic analysis was used to analyse the interviews. Results Four themes were identified: antibiotic prescribing practices and antimicrobial resistance; clinical indicators for prescribing antibiotics, with the sub-themes of history taking, presence of infection and bacterial versus viral infection; patient education; and safety and monitoring. These themes provide insight into registered nurse designated prescribers' understanding of their antimicrobial stewardship role and prescribing of antibiotics. Discussion This research found that the registered nurse designated prescribers had an awareness of the importance of their antimicrobial stewardship role in relation to antibiotic prescribing and reducing antimicrobial resistance. Education about antimicrobial resistance and antimicrobial stewardship for this professional group can be effective, but further research is needed to understand their ongoing educational needs.