A base film for pressure-sensitive adhesive tapes and sheets which comprises a tackifier resin; and a pressure-sensitive adhesive tape or sheet which has a film having at least one layer of the base film as a substrate and a pressure-sensitive adhesive layer formed on at least one face of the substrate. Pressure-adhesive tapes or sheets which have excellent effects of undergoing little dimensional change even under heating or with the passage of time, showing good appearance without suffering from gapping, etc. in case of rolled tapes and sustaining stable pressure-sensitive adhesive force. Particularly favorable effects can be achieved in pressure-sensitive adhesive tapes wherein a polyolefin resin is used as the base film and a rubber pressure-sensitive adhesive containing a large amount of a tackifier resin is used as the pressure-sensitive adhesive.