Willingness-to-share is tested in an Ultimatum Game where the participants iteratively play a role of Proposer and Responder shar- ing a virtual amount of money. We test the hypothesis that brain activity associated with small vs. large share offered by the Proposer can be de- tected by event related potentials (ERPs). We observed that differences between wretched and prodigal offers in ERPs latencies, amplitudes and locations appeared along the antero-posterior midline at the time of Pro- poser’s invite to make the offer, that is before the actual offer was made. Differences in ERPs associated with the offered amount of the share were localized at parietal areas when the offer was accepted. We discuss the outcome of these results for reward learning processes.