Purpose: The influence of attention on postural control and the relationship between attention and falling has been reported in previous studies. Although a dual-task procedure is commonly used to measure attentional demand, such procedures are affected by allocation policy, which is a mental strategy to divide attention between simultaneous tasks. Therefore, we examined the effectiveness of salivary a-amylase, which is a physiological method for measuring attentional demand during postural control. Method: Sixteen healthy participants performed a postural-control task using the Balance System, which is a device that can be calibrated to a specific stability level ("Level 1 = least stable" to "Level 8 = most stable"). Levels 1, 2, and 3 were used for this study. Dependent variables measured were overall stability index, which represents the variance of platform displacement in degrees from a horizontal plane; probe reaction time, which was measured using a sound stimulator and recorder; and salivary a-amylase, which was measured using a portable salivary amylase analyzer. Results: As stability level of the test task decreased, both stability index and probe reaction time significantly increased. In addition, we identified a positive moderate correlation between probe reaction time and salivary a-amylase. Conclusions: Our results suggest that salivary a-amylase and probe reaction time reflect the change in attentional demands during a postural-control task and that salivary a-amylase may be an effective tool for evaluating attentional demands during postural control because it is noninvasive and simple to perform.