Nurses face a high level of mental workload while performing their duties. High levels of mental workload can negatively impact nurses. The aim of this research was to determine the relationship between mental workload and burnout levels of intensive care nurses. Descriptive-correlational design has been adopted in this research. The sample consisted of 156 nurses working in the intensive care units of a hospital in the south of Turkey between September and December 2023. Research data were collected with the 'Participant Information Form', which includes socio-demographic characteristics, 'Mental Workload Scale' and 'Maslach Burnout Scale'. Almost all (95.5%) of the nurses participating in the study reported that their mental workload was high. It has been determined that there is a strong positive relationship between mental workload and burnout. According to the regression model obtained from the research, being a woman (β = .165, p = .008) and emotional workload (β = -695, p < .001) are determinants of emotional exhaustion. These variables explain emotional exhaustion at a rate of 50.1% (adjusted R2 = .501). Emotional workload (β = .399, p = .003) is the most important determinant of personal accomplishment. This variable explains 19.0% (adjusted R2 = .190) of personal accomplishment. The most important determinant of depersonalization is emotional workload (β = .324, p < .001). It was determined that this variable explained 24.4% (adjusted R2 = .244) of depersonalization. This research revealed that there is a strong positive relationship between mental workload and burnout and that increasing mental workload can increase burnout. Nurses' risk of emotional exhaustion increases as mental workload increases. Reducing cognitive workload, temporary workload and emotional workload increases the personal accomplishment experienced by nurses. In addition, as temporary workload, emotional workload and performance-related workload increase, the depersonalization experienced by nurses also increases.