The interaction of [(eta-5-C5Me4R)Ru(CO)2]2 (1a: R = Me, 1b: R = Et) with yellow arsenic, As4 affords besides the pentaarsaruthenocenes [(eta-5-As5)Ru(eta-5-C5Me4R)] (2a, 2b) the tetranuclear clusters [{(eta-5-C5Me4R)Ru}3Ru(eta-3-As3)(mu-3-eta-3-As3)(mu-3-As)3] (3a, 3b). The structure of 2b and 3b has been elucidated by X-ray analysis.