Purpose / Context – To quantify the relationship between indoor temperature and blood pressure in Japanese nursing home residents. Methodology / Approach – A field study of 27 nursing homes in Japan was conducted. We meas-ured the indoor temperature of nursing homes and collected data on resident’s blood pressure via a standardised questionnaire. Facilities were classified into two groups based on measured indoor temperature. Blood pressure rise in winter was defined as the difference in blood pressure between January and August to minimise individual variation. Results – Daytime and night-time indoor temperatures were significantly associated with blood pressure rise in winter, even after adjusting for the effects of potential confounders such as age, gender, body mass index, residential period, care level, systolic blood pressure in August, and med-ication in January. A 1 °C decrease in the indoor room temperature was significantly associated with a 0.74 mmHg increase in the blood pressure rise in winter for daytime temperature (p 0.01) and a 0.72 mmHg increase for night-time temperature (p 0.01). Key Findings / Implications – The association between indoor temperature and blood pressure that we found could contribute to controlling the blood pressure of residents by improving indoor thermal environments in nursing homes. Originality – Our findings from this field study on residents in nursing homes expand the applica-bility of previous studies on the general population in real life situations and clarify the generalisa-bility of experimental evidence about thermoregulation and blood pressure in controlled settings.