In this paper, amino acid coated and radiolabeled magnetic nanoparticles (MNPs) were prepared as a potential diagnostic agent. Magnetic nanoparticles were synthesized and functionalized by L-alanine and L-cysteine amino acids in one step. Besides surface functionalization, amino acid coating also provided favourable particle size. Structural characterization was performed by scanning electron microscopy. We obtained 30-38 nm and 22-30 nm diameter ranges with spherical shape for L-alanine and L-cysteine coated nanoparticles, separately. Then L-alanine and L-cysteine coated MNPs were radiolabeled with Tc-99m(I)-tricarbonyl core Tc-99m(CO)(3)-Alanine-MNP, Tc-99m(CO)(3)-Cysteine-MNP) with a labeling yield of 63 +/- 3% and 74 +/- 2%. Pure radiolabeled magnetic particles were obtained by washing them with saline solution, and the radiochemical purity of Tc-99m (CO)(3)-Alanine-MNP and Tc-99m(CO)(3)-Cysteine-MNP were found as 94.3 +/- 0.47% and 97.6 +/- 1.06% in each of the final solution, respectively. In addition, both radiolabeled nanoparticles were stabile up to 4 h at 37 degrees C temperature in vitro conditions.