Synthesis of the hybrid nanoparticles through simultaneous polymerization of organic monomer and solgel process of the inorganic precursor is a promising subject for creating new materials. Herein, an efficient one-pot synthesis method using the simultaneous sol-gel process with free radical polymerization technique reports the tunable morphology for silica/ poly(acrylic acid) (PAA) hybrid nanoparticles in which tetraethoxysilane (TEOS) and acrylic acid were used as inorganic and organic precursors, respectively. To achieve the best conditions for a simultaneous synthesis, the most important parameters such as pH, TEOS concentration, AA/TEOS ratio, surfactant concentration and temperature were adopted with respect to particle size. It is experimentally demonstrated that the reaction temperature is the most influential parameter affecting the particle size of hybrid nanoparticles. In addition, transmission electron microscopy images revealed that, the tunable morphology of hybrid nanoparticles from the organic-inorganic core-shell to organic and inorganic heterodimer nano(semi)spheres can be achieved by controlling the concentration of TEOS.