The present invention provides a rubber composition for covering a carcass cord, which makes it possible to consider an effect on environment, prepare for decrease in supply quantity of petroleum resources in future, reduce rolling resistance and improve rubber strength and processability, and a tire prepared by using the rubber composition. The rubber composition for covering a carcass cord of the present invention comprises 25 to 80 parts by mass of silica, 1 to 15 parts by mass of a silane coupling agent and 3 to 30 parts by mass of an organic vulcanizing agent represented by the following general formula (1): --(R--S.sub.x).sub.n-- wherein R is --(CH.sub.2--CH.sub.2--O).sub.m--CH.sub.2--CH.sub.2--; x is an integer of 2 to 6; n is an integer of 10 to 400; and m is an integer of 2 to 5, based on 100 parts by weight of a diene rubber, and a tire prepared by using the rubber composition.