There is provided an epoxy composition which has difficulty in precipitating a crystal during storage, is homogeneous and can be stored for a long period; and a cured product of the composition having excellent transparency, heat resistance, and light resistance can be obtained on curing. An α-type tris-(2,3-epoxypropyl)-isocyanurate crystal comprising β-type tris-(2,3-epoxypropyl)-isocyanurate in the crystal in a ratio of 2% by mass to 15% by mass. A method for producing the α-type tris-(2,3-epoxypropyl)-isocyanurate crystal comprising step (i) separating β-type tris-(2,3-epoxypropyl)-isocyanurate contained in a tris-(2,3-epoxypropyl)-isocyanurate solution from the solution as a solid to obtain a crystal with an increased content ratio of α-type tris-(2,3-epoxypropyl)-isocyanurate.