A biaxially oriented polyester film wherein the ratio (=I.sub.MD /I.sub.ND) of the peak intensity (I.sub.MD) in the longitudinal direction to the peak intensity (I.sub.ND) in the thickness direction determined at 1615 cm.sup.-1 by laser Raman scattering method is 6 or more; and a process for production of a biaxially oriented polyester film which comprises the steps of controlling the ratio (A/B) of the maximum thickness (A) of the edge portion of a cast film to the thickness (B) of the central portion in the transverse direction thereof in the range of 2 to 6, biaxially stretching the cast film, and controlling the peak intensity ratio of the biaxially oriented film determined by the laser Raman scattering method in the above-described range. The biaxially oriented polyester film thus produced has a specific orientation in the longitudinal direction, and therefore has great strength in the longitudinal direction and small irregularity in properties such as thickness or birefringence.