The main purpose of this study was to determine the effects of aging on the variability of gait over multi-surface terrain. An additional aim was to compare this variability to walking on solid ground. Ten young adults and 10 older adults walked along a walkway which contained a middle portion with multi-surface terrain. This multi-surface terrain consisted of solid, compliant, rocky, irregular, slippery, and uneven surfaces. We examined the effects of the multi-surface terrain and age on measures of variability including step length, step width, trunk pitch and roll, trunk centre of mass (tCOM) acceleration, and head acceleration. Step, trunk, and head variability were increased on the multi-surface terrain as compared to solid ground for both young and older adults (p<0.05). Older adults demonstrated larger medial-lateral tCOM acceleration RMS (p=0.0004) and trunk roll RMS (p=0.0001) when walking on the multi-surface terrain. In addition, older adults also walked more slowly (p=0.002) and took shorter steps (p=0.003). However, there were no age-related differences in step variability. The results suggest that multi-surface terrain poses a greater challenge to balance reflected by the increased variability, particularly in older adults.