The phase transformation from beta-Ag3SI with Pm3m to alpha-Ag3SI with Im3m occurs with an order-disorder transition of anions. This observation was discussed on the base of the local anion ordered structure in alpha-Ag3SI at 519 K. On the beta-alpha transformation, abnormally large lattice expansion of alpha-Ag3SI was observed in a temperature range of 520 K to 590 K. Structure refinements of alpha-Ag3SI were carried out at high temperatures above 590 K and the weighted R values were in a range between 0.027 and 0.041. Structure analysis was also carried out at 153 K on the alpha-Ag3SI crystal which was obtained by quenching to 153 K from 703 K. These structure analyses revealed that Ag ions in alpha-Ag3SI statistically distribute on 8c and 24g sites with Ag occupancies of about 0.07 and 0.10, respectively.