Aim Polypharmacy, which is often observed in elderly patients, has been associated with several unfavorable outcomes, including an increased risk of potentially inappropriate medications, medication non‐adherence, drug duplication, drug–drug interactions, higher healthcare costs and adverse drug reactions. A significant association between polypharmacy and adverse outcomes among older people living in the community has also been confirmed. A reduction in the number of medications should thus be pursued for many older individuals. Nevertheless, the factors associated with polypharmacy in elderly home‐care patients have not been reported. Here, we investigated those factors in elderly home‐care patients in Japan. Methods We used the data of the participants in the Observational Study of Nagoya Elderly with Home Medical investigation. Polypharmacy was defined as the current use of six or more different medications. We carried out univariate and multivariate logistic regression analyses to assess the associations between polypharmacy and each of several factors. Results A total of 153 home‐care patients were registered. The mean number of medications used per patient was 5.9, and 51.5% of the patients belonged to the polypharmacy group. The multivariate model showed that the patients’ scores on the Charlson Comorbidity Index and the Mini‐Nutrition Assessment Short Form were inversely associated with polypharmacy, and potentially inappropriate medication was most strongly associated with polypharmacy (odds ratio 4.992). Conclusions The present findings showed that polypharmacy was quite common among the elderly home‐care patients, and they suggest that home‐care physicians should prescribe fewer medications in accord with the deterioration of home‐care patients’ general condition. Geriatr Gerontol Int 2017; ••: ••–••.