A facile template method was employed to synthesize Fe nanowires of different sizes, dimensions. Comprehensive analyses were conducted to explore their morphology, structure, composition, and magnetic properties. The surface of as-prepared Fe nanowires was modified with SiO by sol-gel method to improve the dispersion of as-prepared Fe nanowires in aqueous solution. Furthermore, the relaxation properties, biocompatibility and in vivo imaging abilities of the Fe@SiO nanowires were evaluated. The study revealed that the SiO-coated Fe nanowires functioned effectively as transverse relaxation time (T) contrast agents (CAs). Notably, as the length of the Fe@SiO nanowires increased, their diameter decreased, leading to a higher the transverse relaxivity (r) value. Our study identified that among the Fe nanowires synthesized, the Fe3@SiO nanowires, characterized by a diameter of around 30 nm and a length of approximately 500 nm, exhibited the highest r value of 59.3 mM s. These nanowires demonstrated good biocompatibility and non-toxicity. Notably, upon conducting small animal imaging a 1.5 T with Sprague-Dawley rats, we observed a discernible negative enhancement effect in the liver. These findings indicate the promising potential of Fe@SiO nanowires as T CAs, with the possibility of tuning their size for optimized results.