A newly designed ultrasmall total internal reflection prism with a size of 29\text{\hspace{0.17em} mm}\times \text{22 \hspace{0.17em} mm}\times \text{24 \hspace{0.17em} mm} and weight of \text{19 .5 \hspace{0.17em} 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 \text{48 \hspace{0.17em} mm} and a footprint of \text{80 \hspace{0.17em} mm}\times \text{132 \hspace{0.17em} mm} . By using an overdriving f/\text{2 .0} projection lens, the geometric efficiency of the projection system, {\eta }_{geo\text{-}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 {\eta }_{geo\text{-}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.