This study examined the role of ownership in the endowment effect. It used the Implicit Association Test to investigate the influence of effort cues on psychological ownership and object monetary valuation. It also examined whether factual ownership or loss aversion contributed to the endowment effect. Pariticipants were either given a pen or not and either squeezed a stress ball or held it. They actually sold or purcahsed the pen, giving both selling and buying price for another person and either selling (owner) or buying (non-owner) price for themselves. Results support both loss aversion and psychological ownership but not factual ownership.