The purpose of the present study was to examine the validity and reliability of the stages of change for sedentary behavior scale among workers. The participants were 2400 Japanese workers aged 20-59 years (male: 50.0%, mean age: 40.4±10.8 years) recruited from research company. With an internet-based survey, the stages of change for sedentary behavior, total sitting time (min/day), socio-demographic characteristics, health-related characteristics and work-related characteristics were obtained. “Too much sitting” was defined as sitting or lying down for a total of 8 hours or more per day on average. Participants were categorized into one of 5 stages based on their present status for “too much sitting” and motivational readiness for reducing sedentary behavior. For the criterion validity, a one-way analysis of variance was utilized to compare the total sitting time among the 5 stages. To assess the test-retest reliability, randomly-selected 200 workers answered the scale again two weeks later. Then, the Kappa index (k) was calculated. As results, the means of total sitting time were significantly distinguished across the stages [F (4, 2395) =111.5, p<0.001, η2=0.16]. Participants in early stages (precontemplation, contemplation, preparation) had significantly longer sitting time than those in the Maintenance (Precontemplation>Contemplation, Preparation>Action, Maintenance) (p<0.001). The scale to assess the readiness to reduce sedentary time has shown good 2-week test-retest reliability (k=0.64). These results suggest that the developed scale presented good validity and reliability to assess the motivational readiness for reducing prolonged sedentary behavior among Japanese workers.