  We present an investigation on the large magnetic anisotropy of Fe_{2}P,
based on {\it Ab Initio} density-functional theory calculations, with a full
potential linear muffin-tin orbital (FP-LMTO) basis. We obtain an uniaxial
magnetic anisotropy energy (MAE) of 664 \mu eV/f.u., which is in decent
agreement with experimental observations. Based on a band structure analysis
the microscopical origin of the large magnetic anisotropy is explained. We also
show that by straining the crystal structure, the MAE can be enhanced further.
