Shallow depth-of-field (DoF) and a smooth bokeh are signature elements of Digital SLR cameras and high-quality lenses. Producing comparable effects on mobile platforms has long been challenging due to small sensor sizes and short focal lengths of mobile cameras. In this paper, we exploit depth sensing capabilities on emerging mobile devices and develop a new depth-guided refocus synthesis technique particularly tailored for mobile devices. Our technique takes coarse depth maps as inputs and applies novel depth-aware pseudo ray tracing. The depth maps can be obtained from mobile depth sensors, mobile stereo cameras and even from user-inputs. Our pseudo ray tracing scheme resembles light field synthesis and refocusing [21] but does not require actual creation of the light field and hence reduces both memory and computational overhead. At the same time, the scheme can overcome boundary bleeding and discontinuity artifacts observed in previous filtering techniques. Comprehensive experiments show that our approach can produce very high quality DoF comparable to the ones produced by DSLR and the Lytro light field cameras.