Here we report for the first time a very simple, efficient and economical synthetic process for the preparation of mesoporous SiC nanoparticles with highly ordered mesoporous structure and monodispersed rectangular shaped rod like particles through a carbothermal reduction using uncalcined mesoporous silica as a template which was prepared from the static synthesis mode and polycarbosilane (PCS) as carbon precursor. The uncalcined silica template provides enough carbon content in the form of surfactant molecules which are sandwiched between the silica wall and the PCS precursors and enhance the reaction between the carbon and the silica sources to obtain high purity mesoporous SiC. A set of samples were prepared by adding different amounts of PCS in uncalcined mesoporous silica prepared at different temperatures. The textural parameters and the morphology of the materials were obtained by several characterization techniques such as XRD, nitrogen adsorption, HRSEM, HRTEM, FT-IR and thermo gravimetric analysis. Low and high angle XRD results revealed that the amount of PCS addition in the synthesis mixture plays a significant role in controlling the crystallinity of the mesoporous SiC. We also demonstrate for the first time that the pore diameter of the mesoporous SiC can be controlled by the simple adjustment of the synthesis temperature of the uncalcined mesoporous silica template. The pore diameter of the materials can be tuned from 3.0 to 4.4 nm. The measured specific surface area and the specific pore volume of the samples were in the range between 285.2 and 564.4 m² g⁻¹, and 0.24 and 0.66 cm³ g⁻¹ respectively. HRTEM and HRSEM results confirm that the prepared materials exhibit rectangular rod shaped morphology with well ordered mesoporous structure. Among the samples prepared, the sample prepared with a low amount of PCS showed excellent textural parameters which confirm the crucial role of the presence of surfactant molecules in the uncalcined mesoporous silica template and their participation in the reaction. These results reveal that this simple method is not only economical but also energy efficient as it skips several high temperature steps such as high temperature calcination of the mesoporous silica template and saves a huge amount of PCS. We believe that the present route is a significant breakthrough in the synthesis of mesoporous materials and can be extended for the preparation of other mesoporous non-siliceous materials such as carbon nitrides and boron carbon nitrides.