Purpose: : This study aimed to investigate changes in critical nursing activities from 2009 to 2020 and explore the relationship between nurse staffing and such activities in intensive care units. Methods: : A total of 446,445 adult patients admitted to intensive care units in tertiary and general hospitals from 2009 to 2020 were identified using the National Health Insurance claims database. The Critical Nursing Activities Index was calculated based on the following critical nursing activities: ventilator, extracorporeal membrane oxygenation (ECMO), and continuous renal replacement therapy (CRRT). Trend analysis was performed to analyze changes in critical nursing activities over 12 years and to assess linear trends across different staffing levels. Results: : The annual utilization days for ventilators, ECMO, and CRRT, as well as the Critical Nursing Activities Index significantly increased over the study period (p-for-trend＜.001) in tertiary and general hospitals, except for ventilator use in general hospitals. Ventilator, ECMO, and CRRT utilization exhibited a significant upward trend with higher nurse staffing levels (Bonferroni adjusted p-for-trend＜.001). The Critical Nursing Activities Index was significantly higher in hospitals with higher staffing levels compared to those with lower staffing levels (Bonferroni adjusted p ＜.05). Conclusion : The findings underscore the need for improved nurse staffing levels in intensive care units. Government policies should ensure that staffing levels align with critical nursing activities among critically ill patients to uphold the quality of care.