[Object] To provide a bismuth-substituted rare-earth iron garnet crystal film (RIG) which has an insertion loss of less than 0.60 dB and which can be produced in a high yield, as well as an optical isolator. [Solving means] Provided is a bismuth-substituted rare-earth iron garnet crystal film which is grown by liquid phase epitaxy on a non-magnetic garnet substrate represented by a chemical formula of Gd 3 (ScGa) 5 O 12 , wherein the bismuth-substituted rare-earth iron garnet crystal film is represented by a chemical formula of La 3-x-y Gd x Bi y Fe 5 O 12 (provided that 0
