Abstract Starting from SnCl4. hexasila-fenbutatinoxide (2b) [a silicon analogue of the acaricide fenbutatinoxide (2b)] and its derivatives lb and 3b were prepared (SnCl4 → 1b → 2b -> 3b). The distannoxanes 2a and 2b were found to react very easily with H2O to give the corresponding stannols 4a and 4b, respectively. In solution (C6D6 or CDCl3) the equilibria 2a/2b + H2O ⇄ 2 4a/4b were observed (1H NMR). With regard to the system 2a/4a/H2O, this observation is at variance with an earlier report in which the sterically bulky neophyl substituents [C6H5(CH3)2CCH2] are said to prevent the condensation of 4a to give 2a. - 1b -3b were found to be potent acaricides showing activities similar to those of their carbon analogues 1a -3a (test organisms: adult females of Tetranychus urticae Koch)