In this paper, we report the effects of pH and salt on the gelling properties of silica (SiO2) sols and gels which were measured both by dynamic viscoelasticity measurement and by creep test equipment. The network structures built by SiO2 particles formed under different conditions were observed by a scanning probe microscope (SPM). N-2 adsorption measurements were also conducted in order to analyze the characteristics of dried gel powders including specific surface area, pore volume, and pore size distribution. The objective of this study is to characterize the SiO2 sal, gels, and powders obtained by a Y-shaped reactor under different pH and salt conditions. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.