The effect of steam on the micro-phase structure and mechanical properties of different block copolymers used in biomedical devices is investigated via FT-IR, tensile tests and dynamic mechanical analysis (DMA). Steam sterilization, commonly performed on medical devices and simulated in this work, affects the copolymers' morphology, due to high temperature and humidity conditions. FT-IR analysis reveals that steam induces a modification in the crystalline conformations of copolymers with a pre-existing hydrogen bonding network, that is, thermoplastic polyurethanes (TPU) and poly(ether-block-amide) (PEBA), while it does not significantly affect the domain conformation in styrenic block copolymers (SEBS), due to weak interaction with water. As a consequence, relevant changes of the mechanical properties, closely related to the microdomain structure, are found for TPU and PEBA after sterilization, while SEBS mechanical behavior remains stable, as demonstrated by tensile tests and DMA results. For this reason, SEBS is suggested as the best choice in terms of durability in biomedical applications. (C) 2014 Wiley Periodicals, Inc.