A pressure-sensitive adhesive composition which comprises three ingredients, i.e., polyisoprene, a styrene/isoprene/styrene copolymer, and solid polyisobutylene, in a proportion of (10-60)/(10-50)/(20-60) by weight and further contains a non-solid isobutylene polymer and a tackifier, characterized in that the amount of the non-solid isobutylene polymer is 1 to 30 pts. wt., excluding 30 pts. wt., per 100 pts. wt. of the sum of the three ingredients, i.e., the polyisoprene, styrene/isoprene/styrene copolymer, and solid polyisobutylene. When used in an adhesive patch for external use on the skin, the composition has satisfactory tackiness regardless of whether the temperature of the surrounding air is high or low, has excellent long-term storage stability, retains the necessary cohesive force, and does not unnecessarily irritate the skin.