Workers on construction projects have a high risk of accidents, and time constraints require workers to experience physical and mental fatigue. Physical and mental fatigue can reduce attention and weaken reactions when doing work. Physical fatigue has an impact on work safety. Internal and external factors can cause fatigue and work accidents. Internal factors of workers include age, length of service, length of sleep, marital status, nutritional status, and work training. External factors include the work environment, field conditions, and implementation management. This study emphasizes the internal factors of workers that are related to fatigue and work accidents. This study uses primary data from questionnaires. The sampling of respondents used purposive sampling. Respondents for this study were 30 construction workers in the field. The analysis used in this study was the independent t-test. The independent t-test aims to determine the effect of internal factors on fatigue and work accidents. The results showed that internal factors of workers that significantly influenced work fatigue were age, marital status, length of sleep, and length of service. Nutritional status did not significantly influence fatigue. Meanwhile, an internal factor that had a significant influence on work accidents was work training (sig. < 0.05). Internal factors of workers need to be given serious attention so that the risk of work accidents in construction projects can be reduced.