Disclosed herein are a polyamide-imide film which is transparent and exhibits superior mechanical properties such as surface hardness, etc. and a method of preparing the same. The polyamide-imide film a copolymer of an aromatic diamine, an aromatic dianhydride, and an aromatic dicarbonyl compound, wherein the aromatic diamine and the aromatic dianhydride forms an imide unit; the aromatic diamine and the aromatic dicarbonyl compound forms an amide unit; and the amide unit accounts for 50-70 mol % of 100 mol % of the units of the copolymer, thereby exhibiting transparency and superior mechanical properties including surface hardness.