Background Polypharmacy is associated with an increased risk of adverse drug events in older people. Although national guidance on geriatric pharmacotherapy exists in Japan, tools to routinely monitor the quality of care provided by community pharmacists are lacking. Aim To develop a set of quality indicators (QIs) to measure the quality of care provided by community pharmacists in improving geriatric pharmacotherapy in primary care in Japan, using a modified Delphi study. Method The development of QIs for the Japanese community pharmacy context followed a two–step process: national guidance review and consensus testing using a modified Delphi study. The latter involved two rounds of rating with a face–to–face meeting between the rounds. Ten experts in geriatric pharmacotherapy in primary care were recruited for the panel discussion. QIs were mapped to three key taxonomies and frameworks: the Anatomical Therapeutic Chemical (ATC) classification system, problems and causes of drug–related problems (DRPs) taxonomy and Donabedian’s framework. Results A total of 134 QIs for geriatric pharmacotherapy were developed. This QI set included 111 medicine specific indicators, covering medicines in 243 third–level ATC classifications. QIs were classified into the problem of treatment safety (80%) and causes of drug selection (38%) based on validated classification for DRPs. In Donabedian's framework, most QIs (82%) were process indicators. There were no structure indicators. Conclusion A set of 134 QIs for geriatric pharmacotherapy was rigorously developed. Measurement properties of these QIs will be evaluated for feasibility, applicability, room for improvement, sensitivity to change, predictive validity, acceptability and implementation issues in a subsequent study.