Monodisperse dendritic mesoporous silica nanospheres (DMSNs) with enlarged diameter and extremely tiny pore size were synthesized by brominated dodecyl trimethyl ammonium bromide which is a relatively short carbon chain surfactant and acts as template agent. The as-prepared DMSNs-C12 were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourie tansform infrared spectroscopy (FT-IR), N2 adsorption-desorption isotherms to reveal its morphology, crystal texture, chemical compositions, pore volume and specific surface area. The results indicate that the particle size of DMSNs-C12 greatly increases, wrinkled structure disappears and the pore size significantly declines, compared with DMSNs fabricated with conventional cetlytrimethyl ammonium bromide as emplate agent (noted as DMSNs-C16). The reason could be that the mutual repulsive force of surfactants decreases with the reduction of carbon chain which affects microemulsion formation, giving rise to structural difference.