A rubber composition which is effective in improving the reaction efficiency of a silane coupling agent in kneading, suppressing generation of air bubbles, improving processability and abrasion resistance and lowering rolling resistance, and a process for preparing the same, wherein the rubber composition includes silica, 3 to 15 parts by weight of a silane coupling agent based on 100 parts by weight of the silica and 0.3 to 1.45 parts by weight of a potassium salt based on 100 parts by weight of silica.