In this study, we conducted a comprehensive investigation of the effect of aromatherapy intervention with kuromoji (Lindera umbellata), a rarely used Japanese essential oil, on the physiological markers and cognitive functions of older adults who require nursing care and on their nursing care burden. The study included 10 users of day-care services (2 males, 8 females) who provided consent to participate. The participants’ mean age was 82.1±7.0 years. The study design included a control period in which no essential oils were used and an aromatherapy period in which kuromoji aroma was used (each therapy lasting 4 weeks). The study results revealed no significant differences in salivary cortisol marker scores, stress evaluation index, and cognitive function among the experimental periods or between the pre- and post-intervention periods. The nursing burden on facility employees decreased significantly (significance level: 5%) between the post- and pre-intervention periods in the second control period and in the first and second aromatherapy periods. Investigation of vital signs revealed no significant difference in the pulse rate among the experimental periods and between the pre- and the post-intervention periods, but blood pressure (BP) declined significantly (standard of significance: 5%) in the post-aromatherapy intervention period for some systolic and diastolic BP levels. Compared with the control period, the intervention period showed a downward trend in the mean BP levels. The use of kuromoji essential oil in older adults requiring care was found to result in a greater increase in positive emotions and decrease in negative emotions compared to the control group, suggesting that it may have a positive impact on their emotional well-being. Further research is needed to investigate the potential long-term effects on dementia and stress reduction.