The purpose of this study is to investigate the gait improvement for lame patients based on the gait quality index estimated by the spectral analysis results of trunk acceleration. The gait quality index (GQI) is defined as the power spectrum ratio of the total value up to 10 Hz to that of the fw component in the vertical direction where fw is the pace frequency. The hemiplegic patients, patients after total hip arthroplasty, patients with femoral fractures, patient with anterior cruciate ligament injury and Parkinson's disease patients were selected in this study. Dynamic load factor (DLF) corresponding to the vertical walking force is also calculated using power spectrum density for time history trunk signals measured by the accelerometers. When the correlation between DLF and GQI was plotted, it was found that the gait quality index GQI was clearly improved (numerically reduced) for all lame patients as the increase of DLF due to the improvement of the gait. Based on these results, it was confirmed that the value of GQI in the vertical direction was the useful index in order to evaluate the gait improvement for all lame patients.