Abstract: A novel high density magnetic recording medium is disclosed. Said medium comprises a polyester film formed of a plurality of layers laminated by coextrusion and oriented by stretching, which simultaneously satisfies the conditions of the following relations (1) to (4); a back coat layer which is provided on the rougher surface side of said polyester film layer and whose surface roughness simultaneously satisfies the conditions of the following relations (5) and (6); and a magnetic film layer provided on the less rough surface side of said polyester film.Ra.sup.A .ltoreq.0.008 (1)0.005.ltoreq.Ra.sup.B .ltoreq.0.02 (2)0.005.ltoreq.Ra.sup.B -Ra.sup.A .ltoreq.0.015 (3)9.ltoreq.F.sub.5 .ltoreq.30 (4)0.015.ltoreq.Ra.sup.C .ltoreq.0.040 (5)0.003.ltoreq.Ra.sup.C -Ra.sup.B .ltoreq.0.35 (6)whereinRa.sup.A stands for centerline average roughness (.mu.m) of the less rough surface side of the polyester film;Ra.sup.B stands for centerline average roughness (.mu.m) of the rougher surface side of the polyester film;Ra.sup.