To provide a film for a heat-resistant tape substrate suitable for high-precision processing, which has excellent dimensional stability in a roll-to-roll production process, and exhibits high dimensional stability even in the case of using the film obtained by the roll-to-roll process as a heat-resistant tape for mounting or masking e.g. in a capacitor production process.

The polyester film for the heat-resistant tape is a biaxially oriented film composed mainly of polyethylene naphthalene dicarboxylate, and has a longitudinal thermal shrinkage of the film of ≥1.2% and ≤3.0% and a lateral thermal shrinkage of ≥0.1% and ≤1.5% after heating the film at 200°C for 10 min, a longitudinal Young's modulus of the film of ≥6,500 MPa, and a film density of ≥1.3580.