Kin discrimination has often been investigated in the context of cannibalism, where differential treatment of kin may entail inclusive fitness benefits if closely related conspecifics are spared during foraging. Competition between related individuals can greatly modify the fitness benefits of such behaviour, but its effect has rarely been tested. In this study, we investigated how two competition-related parameters, that is, the actor's relatedness to the competitors of the recipient individual (rxe) and the general decrease in fitness among these competitors originating from the altruistic act (d) influence egg-cannibalism in smooth newts, a facultatively cannibalistic species. We found that only 29% of the observed 31 females performed cannibalistic attempts after fasting, when kin and non-kin eggs were offered for consumption. These individuals attacked their own eggs less frequently than other conspecific eggs when kin ratio among the offered eggs (parameter rxe) was low, but showed no discrimination when the ratio of kin was high. On the other hand, the total number of eggs (as a proxy for parameter d) did not affect the females' kin discriminative behaviour significantly. These results provide the first evidence for kin discrimination during egg-cannibalism in the smooth newt, and support the significance of kin competition for the evolution of altruism.