An X-ray study of three phase transitions (PTs) at 86, 78 and 72 K has been carried out for the trigonal modification of the Cs3Sb2I9 crystal (space group P-3m1, a = 8.460 Angstrom, c = 10.398 Angstrom). The T-c1 = 86 K PT preserves the trigonal symmetry and is associated with the doubling of the c-parameter. At T-c2 = 72 K a doubling of a and b is observed. An intermediate incommensurate phase with q(1) = 1/2c*, q(2) = (1/2 - delta)a* + 1/2c* has been detected in the temperature range of 78-72 K. The lock-in PT at 72 K has a first order character. (C) 1999 Published by Elsevier Science Ltd. All rights reserved. [References: 4]