Abstract This paper focuses on the influence of Y on the stress rupture properties of a Ni-based superalloy. It also gives reasons for stress rupture life decrease caused by excessive Y doping. It has been shown that the stress rupture lives are strongly dependent on Y concentrations. The stress rupture is low for the undoped alloy and increases through a maximum from 0.009 to 0.014wt.% Y. The microstructures of the alloys have been studied by means of SEM, TEM and EDS. When an excessive amount of Y is introduced, some BCC structured Al2Ni6Y3 phases precipitate in the vicinity of the grain boundaries. Fractographic evaluations reveal that cracks originate around Al2Ni6Y3, leading to premature failure of the stress rupture specimens. There is also some fine cubic γ′ within the Al2Ni6Y3 phase.