The transmission of bacteria and viruses in ligament transplants should be prevented by sterilization. In this study, the influence of two different methods on the mechanical properties of a freeze-dried medial collateral ligament was analyzed in sheep. Group I (n = 10) was treated with irradiation (26 kGy) and group II (n = 10) with ethyleneoxide. The mechanical properties changed in respect of the maximal load: group I (-29.9%; P < 0.05), group II (-7.7%), elongation: group I (-6.6%), group II (-0.3%), stress: group I (-20.1%), group II (-6.8%), strain: group I (-0.64%), group II (-0.3%), stiffness: group I (-10.2%), group II (-10.5%), energy: group I (-31.4%), group II (-6.9%) and elastic modulus: group I (-1.3%), group II (-5.0%). The irradiation dose significantly reduced the maximal load, whereas ethyleneoxide sterilization resulted only in minor changes. Because of the potential cancerogenity of ethyleneoxide, a close monitoring of aeration times and its residuals are very essential. Further studies with lower irradiation doses of between 15 and 26 kGy seem to be justified.