The present study aimed to investigate Theory of Mind (the ability to infer others' mental states) deficit in 20 patients with mild Alzheimer's disease and with 20 healthy controls, with two Theory of Mind tasks, one of them being a real interactive task. Previous results concerning preserved or altered Theory of Mind abilities in Alzheimer's disease have been inconsistent and relationships with other cognitive dysfunctions (notably episodic memory and executive functions) are still unclear. Method: The first task we used was a false belief paradigm as frequently used in literature whereas the second task, a referential communication task, assessed Theory of Mind in a real situation of interaction. Participants also underwent neuropsychological evaluation to investigate potential relationships between Theory of Mind and memory deficits. Results: The results showed that Alzheimer patients presented a genuine and significant Theory of Mind deficit compared to control participants characterized notably by difficulties to attribute knowledge to an interlocutor in a real social interaction. Conclusion: These results further confirm that Theory of Mind is altered in early stages of Alzheimer dementia which is consistent with previous works. More specifically, this study is the first one to objectivize this impairment in social interaction.