A newly designed ultrasmall total internal reflection prism with a size of 29 mm × 22 mm × 24 mm and weight of 19.5 g is proposed for use in a pocket-sized Digital Micromirror Device projector. The entire projector, including an arc lamp illumination, relay, and projection system, has a height of 48 mm and a footprint of 80 mm × 132 mm. By using an overdriving f/2.0 projection lens, the geometric efficiency of the projection system, ηgeo-pro, can be enhanced from 80% to 92%. Although, at the same time, the contrast decreased from 1200:1 to 500:1, this can be enhanced using an off-axis stop. By tuning the position of the stop, the contrast can be as high as 3700:1 for a ηgeo.pro equal to 90%. Using what we believe to be a novel prism design, we can get a very compact optical system with a high efficiency and good contrast ratio.