We demonstrate a novel type of ZnO self-powered photodetector based on the asymmetric metal-semiconductor-metal (MSM) structure: one Au interdigitated electrode with wide fingers and the other one with narrow fingers. These ZnO photodetectors exhibit attractive photovoltaic characteristics at 0 V bias. More interestingly, with increasing the asymmetric ratio (the width of wide fingers : the width of narrow fingers) of the interdigitated electrodes, the responsivity of the ZnO self-powered UV photodetectors was enhanced obviously, reaching as high as 20 mA W⁻¹ when the asymmetric ratio was 20 : 1. A physical model based on band energy theory was developed to illustrate the origin of the photoresponse at 0 V in our device. Our findings provide a new route to realizing self-powered photodetectors.