The triglyceride (TG)/high-density lipoprotein cholesterol (HDL-C) ratio is related to insulin resistance (IR). However, little information is available on whether TG/HDL-C is associated with IR and components of metabolic syndrome (MetS) and how lifestyle habits affect TG/HDL-C in the healthy Japanese population. In total, 1068 Japanese subjects who had undergone an annual health examination and who were not receiving medication were recruited. Determinants for TG/HDL-C ratio were investigated using multiple regression analyses. The subjects were divided into three groups by lifestyle habits (, smoking, exercise, and physical activity), homeostasis model assessment of IR (HOMA-IR), and fasting plasma glucose, four groups by alcohol intake, and five groups by numbers of MetS components to compare TG/HDL-C values. All analyses were done separately by sex. Multiple regression analyses revealed that waist circumference and smoking were positively associated with TG/HDL-C in both men and women, whereas physical activity was negatively associated with TG/HDL-C ratio in women. TG/HDL-C increased with increasing number of MetS in both men and women. TG/HDL-C increased as HOMA-IR increased in both men and women, when subjects were stratified according to HOMA-IR. TG/HDL-C values were lower in both men and women who exercised regularly, had high physical activity, or were nonsmokers. Independent of exercise and physical activity, TG/HDL-C was higher in smokers than in nonsmokers for both men and women. The relationship between TG/HDL-C and alcohol intake was not statistically significant in both men and women. The TG/HDL-C ratio is associated with IR, components of MetS, exercise, physical activity, and smoking, but not alcohol intake, in healthy Japanese subjects.