A CMP slurry is provided comprising polishing particles, the polishing particle comprising organically modified colloidal silica. Also, a method of preparing a CMP slurry is provided, comprising the steps of: preparing polishing particles comprising organically modified silica; converting the polishing particles into an aqueous state; and adding pure water, a hydrophilic additive and a dispersing agent to the polishing particles. The polishing particles can be synthesized using a sol-gel process. According to the invention, a slurry having excellent polishing properties can be prepared, in which the surface properties of colloidal silica are changed to control the physical properties of the polishing particles and which can ensure a desired CMP removal rate while minimizing the occurrence of scratches.