Stable isotope analysis is used to investigate the trophic ecology of organisms and, in order to use samples from archived collections, and it is important to know whether preservation methods alter the results. This study investigates the long-term effects of four preservation methods on sea stars isotopic composition and isotopic niche parameters.We assessed effects of preservation method (freezing, drying, formaldehyde, ethanol) and duration (0, 1, 3, 6, 9, 12 and 24 months) on the stable isotope ratios of carbon, nitrogen and sulfur of sea star tissues. Isotopic ratios were measured using CF-EA-IRMS. We also monitored the evolution of commonly used ecological metrics (isotopic niche parameters) throughout the experiment.Clear changes of δ C values were observed for samples stored in formaldehyde and ethanol. None of the preservation methods had significant or consistent effects on δ N values. Formaldehyde induced a decrease of δ S values. All these changes could be mitigated using correction factors. Isotopic niches parameters slightly changed over time when computed with δ C and δ N values, but inconsistent variations occurred when computed with δ C and δ S values.Overall, these results show that preservation may affect the stable isotope ratios of sea stars. Correction factors can be used to mitigate the effects of the preservation method on stable isotope ratios. Isotopic niches parameters are overall unchanged. Consequently, in most cases, museum samples are suitable to calculate isotopic niche parameters.