Twomey＇s non-linear iteration method is applied to retrieve a particle size distribution from the sedimentation curve measured with a sedimentation balance method. The optimum power, p of weighting function and capability of shortening the measurement time are investigated numerically based on the log-normal and bimodal distributions. It is found that the appropriate value of power, p is 0.7 similar to 2 in most cases. Furthermore it is clarified that the non-linear iteration method can predict size distributions to a certain extent in the case of shortening a measurement time. In order to predict the log-normal distribution accurately, a measurement time longer than the settling time of the mass median diameter of tested powder is required. Based on these results, the size distributions were measured by a sedimentation balance for fly ash and glass beads. As a result, we can predict size distributions of these powders accurately after less than 30 minutes measurement.