Porous silica-based particles with relatively larger average diameter of 1 micron or more and a low particle density are prepared. The method includes the steps of (a) preparing two-layer separated liquid including an organic silicon compound layer and a water layer, then adding an organic solvent, an alkali, and a surfactant into the water layer while agitating at least the water layer so that the organic silicon compound layer and the water layer are not completely mixed with each other, further hydrolyzing and/or partial hydrolyzing the organic silicon compound in the mixed aqueous solution to prepare silica-based particle precursors, (b) adding sodium aluminate into the mixed aqueous solution containing the silica-based particle precursors and then preparing silica-based particles having pores, cavities or voids inside the particles, and (c) washing and drying the silica-based particles. The particles are useful for various applications such as microcapsules, adsorbents, catalysts, and so on.