Background With a rapidly aging population, there is an increasing need for do-not-resuscitate (DNR) and advance care planning (ACP) discussions. This study investigated the factors associated with signing DNR documents of older patients in the geriatric ward. Methods We conducted a retrospective cohort study at a geriatric ward in a tertiary hospital in Southern Taiwan. Three hundred and thirty-seven hospitalized older patients aged ≥65 years in the geriatric ward from 2018 to 2019. The Hospital Information System and electronic medical records were accessed to obtain details regarding patients’ demographics, daily living activities, serum albumin level, nutrition screening score, intensive care unit transferal, resuscitation procedure, days of hospital stay, and survival status on discharge, and DNR status was recorded retrospectively. Patients were classified into DNR and non-DNR groups, with t-tests and Chi-square tests applied to compare the differences between groups. Logistic regression was performed to predict factors related to the DNR documents. Results A total of 337 patients were included, 66 of whom had signed a DNR during hospitalization. After multivariate logistic regression, age 85 or more compared to age 65–74 (adjusted odds ratio, aOR 5.94), poor nutrition with screening score two or more (aOR 2.71), albumin level less than 3 (aOR 3.24), Charlson Comorbidity Index higher than 2 (aOR 2.46) and once transferred to ICU (aOR 5.11) were independently associated with DNR documentation during hospitalization. Conclusions Several factors related to DNR documents for geriatric patients were identified which could provide clinical information for physicians, patients, and their families to discuss DNR and ACP.