The total charge of Sb2O5 is 0. Let x be the oxidation number of antimony. Since there are 5 oxygen atoms each with an oxidation number of -2, we can write the equation:

2x + 5(-2) = 0

2x - 10 = 0

2x = 10

x = 5

Therefore, the oxidation number of antimony in Sb2O5 is +5.