Applying the standard renormalization program to the SU(5) model of Georgi and Glashow we find all O(α) corrections to sin 2 θ w . The O(α) corrections depend on r = M 2 gF /M 2 W , the ratio of the light Higgs mass 2 to the W-boson mass 2 , and on the generation number n g . These corrections are very insensitive to variations of r . Values of these nonleading O(α) corrections near the W-boson threshold for various generation numbers n g are given. For three generations of fermions these corrections do not affect the values of sin 2 θ w by more than 2% provided that all fermions have masses m 2 f ⪡ M 2 W .