Nanocrystalline Fe-Sm-O thin films were prepared by RF magnetron reactive sputtering method in $Ar+O_2$mixed atmosphere with the $O_2$content of 5%. The compositions of the thin films were changed by changing the number of $Sm_2O_3$ chips. The best soft magnetic properties of the thin film with the composition of $Fe_{83.4}Sm_{3.4}O_{13.2}$ were saturation flux density of 18 kG, coercivity of 0.82 Oe and effective permeability about 2,600 at 0.5~100 MHz, respectively. The electrical resistivity of Fe-Sm-O thin films was increased with increasing the amount of Sm and O elements which combined each other, the electrical resistivity of$Fe_{83.4}Sm_{3.4}O_{13.2}$ thin film was $130{mu}{Omega}cm$. In case of the small amount of Sm and O elements, the microstructures of Fe-Sm-O thin films showed a precipitated phase of $Sm_2O_3$ on the ${alpha}-Fe$ phase. With the increase of the amount of Sm and O elements, the microstructures of the Fe- Sm-O thin films were changed into a mixed structure of ${alpha}-Fe$ crystal-phase and Sm-oxide amorphous phase. The Fe-Sm-O thin films with Fe content in the range of 72~94 at% exhibited the quality factor (Q = $mu$′/$mu$") of 7~75 up to 50 MHz.