A pressure sensitive adhesive composition comprising, as a rubber component solid at ordinary temperature, from 10% by mass or more to less than 50% by mass of polyisoprene, from more than 50% by mass to 90% by mass or less of a styrene-isoprene-styrene block copolymer and 0 to 30% by mass of polyisobutylene, and further comprising, per 100 parts by mass of the solid rubber component, 1 to 30 parts by mass of polyisobutylene liquid at ordinary temperature, 50 to 120 parts by mass of a tackifier, and 1 to 40 parts by mass of a plasticizer liquid at ordinary temperature; and a pressure sensitive adhesive tape comprising a base material and the above-described pressure sensitive adhesive composition provided on the base material.