The purpose of this study was to determine whether trunk stability while walking changes when arm swing is deliberately altered in elderly individuals. Participants included 21 community-dwelling elderly individuals (7 men and 14 women; age, 81.8±5.0 years). We measured trunk acceleration by using a wireless miniature sensor unit containing a tri-axial linear accelerometer under 3 walking conditions: normal walking (normal condition), deliberately walking without any arm swing (no swing condition), and walking with a deliberately emphasized arm swing (over swing condition). To evaluate trunk stability during walking, we calculated harmonic ratios (HRs) based on trunk tri-axial acceleration signals (anteroposterior: AP, vertical: VT, and mediolateral: ML). HR–AP and HR–VT were not significantly different across the 3 conditions, but HR–ML in the over swing condition was significantly higher than that in the other 2 conditions by generalized estimating equations (GEE) adjusted for walking speed (p<0.05). These findings indicate that trunk stability in the ML direction increased when the elderly individuals walked with a deliberately emphasized arm swing.