[Objects] Provided is an ionomer resin composition that, when molded into a film shape, is small in both of orientational birefringence and photoelastic birefringence and excellent in transparency, heat resistance, flexibility, and size stability. Additionally, provided are an optical film including the ionomer resin composition, a polarizing plate including the optical film, and a liquid crystal display apparatus including the same.[Solution] An ionomer resin composition according to the present invention is an ionomer resin composition obtained by reacting an acrylic thermoplastic resin (X) including a chain alkyl (meth)acrylate unit (a), an N-substituted maleimide unit (b), and an unsaturated acid and/or unsaturated acid anhydride unit (c) with a metal compound (Y), in which the acrylic thermoplastic resin (X) includes the chain alkyl (meth)acrylate unit (a), the N-substituted maleimide unit (b), and the unsaturated acid and/or unsaturated acid anhydride unit (c) in a total amount of 80% by mass or more, and contents of the structural units (a), (b), and (c) with respect to 100 parts by mass in total of the acrylic thermoplastic resin (X) except for the unsaturated acid and/or unsaturated acid anhydride unit (c) are from 65 to 87 parts by mass, from 1 to 30 parts by mass, and from 0.1 to 5 parts by mass, respectively.