Provided is an adhesive sheet having an adhesive layer formed of an adhesive composition that contains 100 parts by mass of a polyisobutylene-based resin (A) having a weight-average molecular weight of from 270,000 to 480,000, from 5 to 55 parts by mass of a polyisobutylene-based resin (B) having a weight-average molecular weight of from 100,000 to 250,000, and from 10 to 55 parts by mass of a hydrogenated petroleum resin (C) having a softening point of from 90 to 135°C; and provided is an adhesive sheet having at least one adhesive layer wherein the probe tack of the adhesive layer, as measured at a peel rate of 600 mm/min according to JIS-Z0237 (1991), has two maximum values and wherein the first maximum value P1 detected first is at least 4.0 N and the ratio of the second maximum value P2 detected secondarily to the first maximum value P1 [P2/P1] is from 0.25 to 1.50. The adhesive sheets have excellent adhesion force and retention force, can prevent occurrence of zipping, have a low moisture vapor transmission rate, are excellent in transparency and can retard outgas generation.