After a nerve block, observation of the course of effects is necessary until discharge of patients. Particularly epidural block in the lumbar region markedly affects ambulation and postural stability. Although there are few methods of objective evaluation of the postural stability, safe and early discharge is desired. We evaluated the influences of epidural block with 5 ml of 1% lidocaine on equilibrium before as well as 30, 60 and 90 minutes after epidural block. Computerized posturography allows the objective evaluation and quantitative assessment of impairment of receptors and the central nervous system involved in the maintenance of postural stability by analyzing of results. Locus length per unit area with the eyes open and that with the eyes closed 30 minutes after epidural block (27.339±11.761 cm and 25.804±10.561 cm, respectively) were significantly (P=0.0067 and 0.0175, respectively) higher than baseline values (19.528±8.240 cm and 19.496±7.450 cm, respectively). Sway area with the eyes open 30 minutes after epidural block (3.923±2.494 cm²) was significantly (P=0.0190) larger than the baseline value (2.533±1.309 cm²). These results suggest that marked effect remain after epidural block even when standing appears to be stable, and the observation of the course of effects after epidural block is still necessary for the safety of patients. We considered that locus length per unit area is a useful parameter for the assessment of an early discharge.