Gadolinium (Gd) nanoparticles hold significant promise in medical theranostics due to their unique properties. This review outlines the synthesis, characterisation, and applications of Gd nanostructures in combating microbial threats and advancing cancer theragnostic strategies. Synthesis methods such as co-precipitation, microemulsion, and laser ablation are discussed, alongside TEM, SEM, and magnetic characterisation. The antimicrobial efficacy of Gd nanostructures, their potential in combination therapy, and promising anticancer mechanisms are explored. Biocompatibility, toxicity, and regulatory considerations are also evaluated. Challenges, future perspectives, and emerging trends in Gd nanostructure research are highlighted, emphasising their transformative potential in medical applications.