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Despite the widespread use of the superelastic nitinol wires in various industries, there exists a critical understanding gap regarding the relationship between wire diameter and fatigue behavior. This study aims at bridging this gap through a systematic, experimental investigation. During the wire drawing process, which is commonly employed to produce smaller wires, microstructural damage is introduced to the material. Microstructural inhomogeneities affect the phase transformations and also serve as fatigue crack initiation sites. Through microstructural analysis and low-cycle fatigue tests on nitinol wires of varying sizes, we confirmed that wire size significantly influences superelastic properties and fatigue response. Smaller wires exhibit better functional performance but are more vulnerable to surface defects, while larger wires experience greater microstructural damage. These findings highlight the need for careful control of wire size and microstructure in designing nitinolbased devices.