Abstract: We shall overview some properties of algebraic integers and Pisot numbers in A. Garsia, Arithmetic properties of Bernoulli convolutions, Transactions of the American Mathematical Society, Vol. 102, No. 3 (Mar., 1962), pp. 409-432, and present some results of K.S. Lau, S.M. Ngai and H. Rao, Iterated function systems with overlaps and self-similar measures. Journal of the London Mathematical Society (2001), 63: 99-116.