Total knee arthroplasty significantly influenced gait parameters and the variability of gait. The aim of this research was to analyze the effect of total knee arthroplasty (TKA) on balancing ability after sudden perturbation in the early postoperative period. Balancing ability after sudden perturbation was modeled by a provocation test and characterized by the Lehr's damping ratio during double leg and single leg stance. 10 patients operated on by conventional total knee arthroplasty were investigated by the provocation test before TKA and 6 and 12 weeks after TKA and their results were compared with the results of 20 healthy elderly subjects. The results of testing during stance on the affected limb in patients differed significantly from the results of standing on both limbs and on the unaffected limb in the early postoperative period. These results indicated that TKA significantly decreased balancing ability on the affected side after sudden perturbation. Our results showed that 12 weeks after TKA, balancing ability after sudden perturbation improved compared to the results prior to surgery, although it did not return to normal. Deterioration in balancing ability after sudden perturbation can increase the risk of falling.