Purpose The Aim of this study was to investigate the activation time of trunk muscles and characteristics of the movement of center of pressure (COP) during arm swing with a light weight in standing. Methods Thirty health subjects (14 males, 16 females) participated in this study. Arm swing was performed for 10 trials without and with a weight at 1.2Hz frequency toward anterior and posterior direction. Electromyography (EMG) was used to determine muscle activation time and Biorescue was used to measure characteristics of the movement of COP. Surface bipolar electrodes were applied over the right anterior deltoid, the right latissimus dorsi, both rectus abdominis, both internal oblique, and both erector spinae. The data were analyzed by repeated oneway ANOVA and Duncan's post hoc. Results The results were as follows: There were significant differences with muscle activation time in all muscles except the ipsilateral internal oblique between conditions of arm swing without and with a weight (p<0.01). There were significant differences with characteristics of the COP (sway area, length, and speed) between conditions of arm swing without and with a weight (p<0.01). Conclusion The arm swing with a light weight evokes the more rapid EMG activity of ipsilateral trunk muscles and the increasing movement of COP. The findings highlight the importance of investigating the role of the light weight during arm swing in anticipatory postural adjustment and posture stability in maintaining control of vertical posture.