We investigated the effects of trunk twist on postural stability during manually handling flat ties. Ten male subjects participated in this study. While handling 5kgf and 10kgf bundles of flat ties respectively, their centers of pressure (COPs) were measured under two levels of body position (twisted and fixed), two levels of direction (left and right), and three levels of object position (30˚,45˚ and 60˚). Subjects' postural stability was quantified by calculating the sway length. Results showed that the effect of different object position was significant on postural sway length in subject's medio-lateral axis. Post-hoc multiple comparions revealed that, under the 5kgf load condition, the sway length was increased significantly as the object position increased to 45˚. Under the 10kgf load condition, however, the sway length was increased significantly at the object position of 60˚. Actual or potential applications of this research include guidelines for the design of working posture evaluation techniques.