Abstract: An epoxy resin composition for sealing a photo-semiconductor element, comprising(A) an epoxy resin,(B) a curing agent and(C) a polyether-modified silicone oil which is represented by the following general formula (1) ##STR1## wherein m, n and a are each independently a number of 1 or more, b is 0 or a positive number, and R is an alkyl group of 1 to 6 carbon atoms or H,and has a weight average molecular weight of 1,000 to 100,000, a silicone unit content {[(m+n+2)/(m+n+2+a+b+1)].times.100} of 10 to 60% and a polyether unit content {[(a+b+1)/(m+n+2+a+b+1)].times.100} of 40 to 90%and a photo-semiconductor device produced by sealing a photo-semiconductor element with the epoxy resin composition.