Research has shown that increased physical activity is associated with reduced risk of cardiovascular mortality in middle-aged women. Understanding physical activity pattern of middle-aged women is important in terms of designing effective physical activity intervention to increase the level of physical activity. The purpose of this study was to examine hourly ambulatory patterns for middle-aged working women. A total of 106 sedentary women in Seoul, Korea, were recruited for this study (mean age = 27.2±3.1 yrs.; BMI = 20.0±1.9 kg/m2). The number of steps was measured by Yamax pedometer (SW-650), and the step count data were collected through the cell phone and text messaging every hour from 9am to 10pm over seven days, including weekend days (i.e., 5 weekdays and 2 weekend days). Descriptive statistics, including steps mean and standard deviation, were calculated by the whole week and by the type of days (i.e., weekdays and weekend days). In addition, tests of within-subject contrast (polynomial) using SPSS were analyzed in order to determine the trends of hourly ambulatory patterns. Middle-aged women's average number of steps per day was 8,327 (SD = 2,150). Weekdays' average number of steps per day (Mean ± SD; 9,041 ± 2,391) was higher than that of weekend days (6,541 ± 3,254). The average number of steps per hour was 588 ± 128 in weekdays and 477 ± 87 in weekend days. The highest average number of steps per hour was recorded between 9pm and 10pm (791 steps/hour) in weekdays and 5pm and 6pm (614 steps/hour) in weekend days. Tests of within-subject contrast (polynomial) results showed that the hourly ambulatory patterns for sedentary women were somewhat linear as gradually increased shape in weekdays and quadratic as inversed U shape in weekend days, respectively. The results from this study can provide valuable information on the present and future health of this population and directions for physical activity initiatives.Keyword(s): exercise/fitness/physical activity, measurement/evaluation, research