The control of trunk movement plays an important role in stabilizing the head during gait. However, the effects of performing dual tasks on trunk movements during gait are unclear. We compared the effects of an arithmetic task and the colored Stroop test on trunk movement during gait in 34 healthy older adults. The participants walked 20 m normally, or while performing serial seven subtractions or the colored Stroop test. Trunk accelerations were measured using triaxial accelerometers attached to the lower and upper trunk and used to calculate trunk attenuation rate (TAR) as the reduction in acceleration from the lower to upper trunk. Both dual task conditions affected the TAR in the mediolateral and vertical directions (p<0.01), but not in the anteroposterior direction. In the mediolateral direction, the decrease in TAR was greater during the serial seven subtractions than during the Stroop test (p<0.01). In conclusion, dual task-related changes of whole trunk movement during gait, particularly in the mediolateral direction, are dependent on the type of additional task.