To prepare large monodisperse silica particles, it is necessary to grow silica seeds without the formation of new silica particles. Described in this paper are investigations of the characteristic aspects of formation of new particles during the growth of silica seeds through the hydrolysis and condensation of tetraethylorthosilicate, Experimental results indicated that with silica particles as seeds, under a given set of reaction conditions and total external surface area of seeds, the smaller the seed particles, the fewer the newly formed particles during seed growth. The larger the total surface area of the seeds, the fewer the newly formed particles during growth with the same diameter particles as seeds, The critical surface area of nucleation increases linearly with the diameter of seeds, Addition of a small amount of NaCl to the breeding solution can dramatically decrease the number of newly formed particles, From these experimental findings, it is believed that under the conditions of formation of new particles, seed growth during the early stage is controlled by diffusion of colloid-unstable condensed species carrying electric charges capable of overcoming electrostatic repulsion.