Gold and platinum bimetallic nanoparticles, Au@PtNPs, have gained attention due to their plasmonic properties. The controlled synthesis of Au@PtNPs involves complex parameters, and the resulting synergy between Au and Pt introduces possibilities for tailoring their properties. This study explores the effects of key-parameters of synthesis (gold core diameters, reaction time, and Pt concentration) on the final properties of Au@PtNPs. Gold nanoparticles of varying diameters were synthesized and used as cores for the reduction of hexachloroplatinic acid, forming a surrounding shell of Pt nanoparticles. The parameters were systematically tuned to understand their impact on morphology, dimension, stability, and plasmonic properties of Au@PtNPs. Increasing Pt precursor concentration resulted in thicker and denser Pt shells, broadening the localized surface plasmon resonance (LSPR) band and improving Au@PtNPs stability. These properties are essential for applications such as photothermal treatment. The synthesis achieved satisfactory products within just 1 h of Pt4+ reduction at mild temperature without using surfactants. Only limited changes in plasmonic properties were observed after 4 h of synthesis, suggesting an optimal reaction period. Manipulating Au core diameter provided LSPR band control, with smaller cores exhibiting greater broadening towards the infrared region. This systematic exploration provided valuable insights for understanding key-parameters governing the synthesis and properties of Au@PtNPs. AuPtNPs PtNPs keyparameters key gold time acid morphology dimension stability shells (LSPR treatment Pt4 surfactants period control region