Compared to conventional mammography, contrast enhanced dual energy mammography (DEM) can improve tumor detection for the population of women with dense breasts. However, currently used iodine-based contrast agents have several drawbacks such as their contraindication for use with renal insufficiency. In this work, we have developed ultrasmall molybdenum disulfide nanoparticles (MoS2 NPs) coated with 2-mercaptopropionic acid (2MPA) for use as a DEM contrast agent with the aims of improved contrast, stability, clearance, and biocompatibility. The successful synthesis of these particles was confirmed using various analytical methods. The ultrasmall size of the particles (2.6 ± 0.4 nm) may allow them to be rapidly cleared from the body through renal filtration and urinary excretion pathways to minimize long-term toxicity concerns. In addition, it was shown that 2MPA-MoS2 NPs are stable for at least 48 hours in water and PBS, have good CT and DEM contrast, and have promise for being biocompatible. These results demonstrate the potential use of MoS2 NPs as an effective contrast agent for DEM.