Balance ability is closely associated with human's physical capability in various aspects from sports performance in athletes, reduced motor functional control in elder people, and the falls in the patients with neurologic disease such as stroke. A good balance evaluation method is therefore quite important and center of pressure (CoP) trajectories measured by a laboratory based force platform (FP) is considered as a gold standard for balance assessment despite its expensive and complicated setup process. This paper investigates the reliability and sensitivity on the CoP measures in healthy young adults using Nintendo Wii Balance Board (WBB) which is a cheaper solution to this problem. Two main parameters used in this study are the mean CoP path velocity (the summation of all the distance between adjacent CoP points, divided by the used time) and the mean absolute CoP sway distance (the mean distance between the CoP point and the mean value of (x, y) (virtual center)), from CoP trajectories (x, y) information. An experiment for acquiring CoP data through WBB was designed and 16 participants were recruited to perform the balance test during quiet standing in two and single leg, under eyes-open and eyes-closed conditions. Paired t-test was performed and the intraclass correlation coefficient (ICC) was calculated in the statistics analysis. The experiment results showed good reliability and sensitivity of WBB in this test.