Phase-pure FeP nanoparticles have been synthesized by the reaction of iron(III) acetylacetonate with tris(trimethylsilyl)phosphine at temperatures of 240−320 °C using trioctylphosphine oxide as a solvent and dodecylamine (DA), myristic acid (MA), or hexylphosphonic acid (HPA) as additional capping groups (ligands). The DA-capped particles prepared at 260 °C have an average diameter of 4.65 ± 0.74 nm with FeP being the only observed crystalline phase. Elemental analyses indicate a high percentage yield of FeP (85%) and are consistent with 12% TOPO incorporation in the product. The addition of MA has results similar to those of the addition of DA, whereas addition of HPA seems to inhibit crystallite growth, resulting in very small (ca. 1 nm) or amorphous particles that are difficult to isolate. Magnetic susceptibility data on DA-capped FeP suggest that the moments within each particle are coupled antiferromagnetically, at least over a short range; however, there is no evidence of a Néel transition, in contrast to bulk FeP. It is likely that the FeP particles produced by this route are too small (ca. 5 nm) relative to the magnetic cell (2.9 nm) for the onset of long-range helical antiferromagnetic order, even at low temperatures (5 K) and fields (0.010 T).