The invention relates to an epoxy resin composition for encapsulation which comprises (A) an epoxy resin, (B) a hardener, and (C) magnesium hydroxide, wherein the magnesium hydroxide (C) comprises magnesium hydroxide particles in the shape of a hexagonal prism which comprises two hexagonal base faces, i.e., a top and a bottom face, parallel to each other and six peripheral faces formed between the base faces, and has a c-axis-direction size of 1.5*10<-6> to 6.0*10<-6> m. This epoxy resin composition for encapsulation is excellent in flame retardancy, moldability, reflow resistance, and reliability including moisture resistance and high-temperature standing characteristics and is suitable for use in encapsulating VLSIs. Also provided is an electronic part device having an element encapsulated with the composition.