Accurate eating time can be used as an index of forage dry matter intake in grazing cows. To develop a method for easily estimating the eating time of dairy cows in a pasture, 8 lactating Holstein cows were fitted with collars equipped with commercial uniaxial accelerometers; namely, the Kenz Lifecorder EX (LCEX; Suzuken Co. Ltd., Nagoya, Japan), and were allowed to graze in a pasture for 4, 8, or 20 h daily for 7 d. The LCEX device recorded the intensity of the physical activity categorized into 1 of 11 activity levels ranging among 0 (no movement), 0.5 (subtle) and from 1 to 9 (1, light; 9, vigorous intensity) every 4 s during the experimental period. The activities of the animals were also video-recorded for 11 h and were manually classified into 7 categories (eating, searching, ruminating, standing resting, lying resting, drinking, and walking) at 4-s intervals. According to the count distribution of the activity levels for the categorized activities, 94.4% of the counts involving eating activity ranged from activity level 1 to 7. On the other hand, most of the counts were activity level 0 or 0.5 when ruminating and resting activities were observed. No records of activity level 8 or 9 were found in any activities. When activity level 1 was used as a threshold for discriminating eating from the other activities, the lowest misclassification rate of 5.5% was observed. With a threshold of activity level 1, the eating times in pasture for cows grazing for 4, 8, and 20 h/d were 142.8, 290.6, and 438.4 min/d, respectively, and the proportions of the time spent in pasture that were made up of eating time were 0.66, 0.67, and 0.38, respectively [the proportion during daytime (8 h of the 20-h grazing treatment) was 0.63 and that at nighttime (12 h of the 20-h grazing treatment) was 0.23]. The use of the LCEX device allows for easy measurement of eating time and facilitates the determination of the pattern of eating activity in pasture for grazing cows.