Abstract: An object of the invention is to provide such an oriented polyester film that has a constant thickness, and is excellent in dimensional stability at a high temperature and dimensional stability to temperature change in a working temperature range. The invention relates to an oriented polyester film containing as a major component of a substrate layer polyethylene -2,6-naphthalene dicarboxylate, being stretched at least in one direction, and having a film thickness of from 12 to 250 ?m, wherein (1) a coefficient of linear thermal expansion ?t at a temperature of from 30 to 100° C. is from 0 to 15 ppm/° C. in both longitudinal and width directions of the film, and (2) a thermal shrinkage rate at 100° C. for 10 minutes is 0.5% or less in both longitudinal and width directions of the film.

Abstract: An object of the invention is to provide such an oriented polyester film that has a constant thickness, and is excellent in dimensional stability at a high temperature and dimensional stability to temperature change in a working temperature range. The invention relates to an oriented polyester film containing as a major component of a substrate layer polyethylene-2,6-naphthalene dicarboxylate, being stretched at least in one direction, and having a film thickness of from 12 to 250 ?m, wherein (1) a coefficient of linear thermal expansion ?t at a temperature of from 30 to 100° C. is from 0 to 15 ppm/° C. in both longitudinal and width directions of the film, and (2) a thermal shrinkage rate at 100° C. for 10 minutes is 0.5% or less in both longitudinal and width directions of the film.