© Mary Ann Liebert, Inc. 2016. Introduction: T'ai chi chuan is a beneficial exercise of improving health and function. Biomechanical insights of t'ai chi chuan are less understood. Objectives: To study t'ai chi gait (TCG), a common form of t'ai chi chuan in order to quantify external knee adduction moment (EKAM) as a key indicator of mechanical loading of the medial compartment of the knee compared with normal walking (NW). Design: A quantitative biomechanics approach to determine peak EKAM for NW and TCG. Results: There were a tri-modal pattern of EKAM during TCG and a bimodal pattern of EKAM during normal walking. In addition, subsequent analysis showed a 25%-47% reduction in peak EKAM during double support phases of TCG compared with NW; the peak EKAM of TCG during single-limb support phase showed significantly higher magnitude than the other two double-support phases. Conclusion: These results indicate that t'ai chi chuan might be a beneficial intervention for reducing the medial mechanical load at the knee joint, particularly during the first double-support phases of TCG, but the special consideration of higher peak EKAM of single-limb support phase is needed during regular t'ai chi chuan practice.