Although ownership is acknowledged to exert a potent influence on various aspects of information processing, the origin of these effects remains largely unknown. Based on the demonstration that self-relevance facilitates perceptual judgments (i.e., the self-prioritization effect), here we explored the possibility that ownership enhances object categorization. The results of 2 experiments supported this prediction. Compared with items owned by a stranger (Expt. 1) or best friend (Expt. 2), those owned by the self were classified most rapidly (i.e., self-ownership effect) in an object-categorization task. To establish the basis of this effect, the processes underlying task performance were interrogated using a hierarchical drift diffusion model (HDDM) approach. Results of these analyses revealed that self-ownership was underpinned by a response bias (i.e., starting point of evidence accumulation). These findings explicate the origin of the ownership effect during object processing.