Abstract: There is disclosed a polyester support which has a flatness index of from 0.01 to 0.07, which is defined by the following formula: Flatness index=(the average value of .DELTA.L in the transverse direction).times.(.DELTA.L range), in which .DELTA.L (%)=100.times.[(longitudinal direction size at 150.degree. C.)-(longitudinal direction size at 30.degree. C.)]/(longitudinal direction size at 30.degree. C.), and .DELTA.L range (%)=[(maximum value of .DELTA.L in the transverse direction)-(minimum value of .DELTA.L in the transverse direction). The polyester support is excellent in flatness and heat-dimensional stability.