Mesoporous silica materials have received much interest due to commercial applications in chemical separations and heterogeneous catalysis. Recent studies have reported via a sol-gel nanocasting technique, monolithic mesoporous silica with wormlike pore framework could be prepared by utilizing room-temperature ionic liquids (RTILs) as templates and solvents. Although previous reports have indicated that the wormlike pores would be formed in the silica, the detailed pore network structure still remained the crucial issues to be resolved. In the present study, we investigated the pore structure in the monolithic mesoporous silica, which was templated by RTIL (1-butyl-3-methyl-imidazolium-tetrafluoroborate). We revealed an open fractal pore network with a branched and self-similar appearance was formed by the aggregation of the individual spherical pores. Transmission electron microscopy micrographs displayed that the disordered wormlike pore framework was formed in the silica. Furthermore, the small angle X-ray scattering profile measured herein further exhibited three distinct regions of power-law scattering on the respective length scales. In the high-q region, the profile followed Power behavior and a power-law of -4 was observed for the surface fractal dimension of 2, manifesting the primary pore with a smooth surface and a spherical appearance. In the intermediate-q region, a power-law of -2.5 (mass fractal dimension of 2.5), indicating an open mass fractal network was formed by the aggregation of the individual primary pores. Moreover in the low-q region, the power-law of -4 was observed for mass-fractal agglomerates of aggregates. With the proceeding analysis of unified equation in terms of two structural levels, the radiuses of gyration of primary pore (Rg1)and its aggregates (Rg2) were fitted as ca. 0.9 nm and 5.5 nm, respectively. For a spherical-model pore, the radius of pore (R) was ca. 1.16 nm; thus, the averaged pore diameter (D) was 2.32 nm. The number of primary pores in a fractal aggregate (degree of aggregation, z) was calculated as ca. 67.