We investigated the prevalence of Masked Obesity (MO) and the correlations between MO and lifestylerelated habits (e.g., exercise habits, dieting habits), dietary habits, energy metabolism, and seasons. The subjects were 131 young Japanese college students. Body composition was measured by bioelectrical impedance method and Resting Metabolic Rate (RMR) was measured by an indirect calorimeter. Subjects with a BMI in the normal range (n=110) were divided into the MO (percentage of body fat to Body Weight [BF]≥30%) and control (C) (BF<30%) groups. Dietary energy and nutrient intakes were calculated from weighed dietary records. A questionnaire on lifestyle habits was obtained individually from the subjects. The percentage of MO was 32% of subjects within normal BMI. The prevalence of MO was the highest in winter, probably due to accumulation of body fat as an adaptation to cold. The MO group had low Fat-Free Mass (FFM) and high BF. RMR of the MO group was significantly lower than that of the C group. The MO group tended to have poor exercise habits, more dieting (restricting calorie intake) experiences and consumed a diet with less vegetables and beans. We concluded that the prevalence of MO was 32%; it was the highest in winter for subjects who had high fat and low FFM. This fact may be due to poor exercise, more dieting experiences and insufficient intake of vegetables and beans. Furthermore, this accumulation of body fat may be partly due to low RMR.