It is very important to take into consideration the distribution of range, range straggling, and lateral spread of ions implanted into semiconductor materials during designing and fabrication of semiconductor integration devices by means of ion implantation. Er ions with energies between 200 and 500 keV are implanted in SOI (silicon-on-insulator) samples. The mean projection range Rp and the range stragglings Rp of Er ions with a dose of 21015 cm-2 implanted in SOI samples are measured by Rutherford backscattering (RBS) technique. The obtained data are then compared with those predicted by TRIM codes. It is seen that the experimental data of Rp agree well with the theoretical values. However, there are great differences between the experimental data and the theoretical values of Rp.