Several risk factors for heatstroke among forestry workers were previously reported, but the effects of lifestyles of the workers on heatstroke symptoms remain unknown. This study examines the effects of lifestyles on heatstroke symptoms among Japanese forestry workers during the summer. We distributed a questionnaire to 97 forestry workers about heatstroke symptoms, hydration, hotness in workplace, lifestyles including food consumption, sleep duration, exercise, alcohol consumption, and smoking, age, and years of forestry service, and measured physical characteristics. The total health score was used as an index of healthy habits. Thirty-seven workers (38.1%) experienced heatstroke symptoms. Heatstroke and asymptomatic groups significantly differed in terms of age, years of forestry service, frequency and volume of hydration, frequency of urination, and perceived hotness. Logistic regression analysis selected the following key variables associated with the development of heatstroke symptoms: years of forestry service, frequency of hydration adjusted by frequency of urination, and total health score. In conclusion, the present study revealed that one third of forestry workers develop some early symptoms of heatstroke during work, and healthy habits reduce the risk of heatstroke in forestry workers.