A series of niobium-containing mesoporous silicas (Nb-MS) with different pore diameters has been synthesized via an acid-mediated route by using different kinds of nonionic triblock copolymers. The effect of the chain length of poly(propylene oxide) (PO) and poly(ethylene oxide) (EO) units on the structure of Nb-MS materials has been studied. The samples were characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), and temperature-programmed reduction (TPR). The pore diameter of Nb-MS increased with increasing the PO chain length in triblock copolymer. The microporosity was not affected by the type of the copolymer used.