Provided is a polyester film for an adhesive tape substrate, which is excellent in blocking resistance and is made thin. A polyester film comprising a polyester resin layer containing first particles having an average particle diameter of 0.5-3.5 microfine m and a cured resin layer on at least one surface of the polyester resin layer, wherein the relationship (t/X) between the thickness (t: Microfine m) of the polyester resin layer and the average particle diameter (X: Microfine m) of the first particles is 0.6 or more. (1) the cured resin layer is a cured product of a cured resin layer composition containing (a) a binder, (B) a crosslinking agent, and (C) second particles. (2) RSM on the surface of the cured resin layer is 3.0 micro m or less

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