To provide a thermosetting composition for sealing an organic EL element that inhibits generation/growth of a dark spot consistently by sealing the EL element without exerting a harmful effect to it and maintains stable light-emitting performance for a long period of time by retaining high permeability.

This composition comprises (A) 100 pts.wt. of a low molecular weight epoxy resin having at least two glycidyl groups and a 200-2,000 molecular weight, (B) 40-150 pts.wt. of a high molecular weight epoxy resin having a bisphenol A or a bisphenol F epoxy backbone and a 20,000-100,000 molecular weight, (C) 0.5-20 pts.wt. of a nitrile group-containing latent imidazole compound based on 100 pts.wt. of the total amount of the (A) and (B) component, and (D) 0.1-10 pts.wt. of a silane coupling agent as main components. The organic EL element is sealed using the composition.