Secondary ion emission from bio-molecular samples bombarded with ion beams was investigated. Emitted ions from arginine amino acid thin films were measured using a time-of-flight method under 10 keY Ar and 500 keY Au ion bombardments. For 500 keY ion irradiation, the molecular ion yield was about 1 X 10-3 molecules/ion, which was 2 orders of magnitude larger than with 10 keY ion irradiation. As there are very few data on sputtering of bio-molecules under sub-MeY-energy range, the present work will contribute to understanding of emission mechanism caused by ion-beam irradiation.