For the purpose of annihilating tumor in body, hematoporphyrin as a photosensitizer was coated onto magnetic particles of $Fe_3O_4$ prepared by coprecipitation which could be concentrated around the tumor by magnetic field. The photosensitizer was applied differently before, during and after adsorbing the 1st surfactant on the particles. Its added amount was $5{ imes}10^{-4}/mol$, and the coating reaction proceeded at temperatures of 60, 70 and 8$0^{circ}C$. The amounts of photosensitizer coated on the magnetic particles were obtained by calculating an optical density with the maximum UV spectrum. As a result of the UV analysis, the coating amount of photosensitizer increased with higher reaction temperatures. When applied at 8$0^{circ}C$ after adsorbing the 1st surfactant, the photosensitizer was coated with a maximum value of $3.8{ imes}10^{-3}/mo1/$ell$$</TEX>. The TGA analysis revealed that the ferrofluids included the particles of 30.115 g/$ell$. It was suggested that the magnetite particles was coated with photosensitizer of $1.26{ imes}10^{-4}/mo1/g$. A small-sized device for magnetic field and light emission was designed, in which LED sheets coverts the permanent magnet of Nd-Fe-B. The LED sheet was connected in series circuit and also protected with a silicon tube. The power was supplied with rechargable battery of 9V and 100-120mA.