Nanoporous spherical silica particles with nanoparticles adhered to their surfaces and mica powder are generally used in cosmetic powders. To analyze the effect of surface-adhered nanoparticles and nanopores on bulk flowability, nanoparticles adhered to silica surfaces were removed by ultrasonic cleaning using water. To investigate the influence of the nanoporous structure of silica, nonporous silica (with a mean particle diameter of 5 mu m) with adhered nanoparticles was used. The bulk flowabilities of the mixtures of mica and silica powder with and without surface-adhered nanoparticles were characterized by using a friction tester and texture analyzer. The coefficient of dynamic friction (CDF) decreased for both the mixed powders due to the removal of nanoparticles. On the other hand, the aggregation strength (AS) increased due to the cleaning of nanoparticles. (c) 2007 Elsevier B.V. All rights reserved.