A sealing resin composition simultaneously having good transparency, resistance to moisture permeability, and adhesiveness resistant to heat and humidity, and a sealing resin composition sheet obtained therefrom. Using a resin composition containing (A) a styrene-isobutylene modified resin and (B) a tackifier resin as a sealing resin composition, a resin composition layer composed of the resin composition may be formed on a support to give a sealing resin composition sheet.