This work was motivated by the unsatisfactory stability of Au₂₅(SG)₁₈ in solution under thermal conditions (e.g. 70–90 °C for DNA melting). Thus, we searched for a better, water-soluble thiol ligand. Herein, we report a one-pot synthesis and investigation of the stability and optical properties of captopril (abbreviated Capt)-protected Au₂₅(Capt)₁₈ nanoclusters. The Au₂₅(Capt)₁₈ (anionic, counterion: Na⁺) nanoclusters were formed via size focusing under ambient conditions. Significantly, Au₂₅(Capt)₁₈ nanoclusters exhibit largely improved thermal stability compared to the glutathione (HSG) capped Au₂₅(SG)₁₈. Both Au₂₅(Capt)₁₈ and Au₂₅(SG)₁₈ nanoclusters show fluorescence centered at 700 nm. The chiral ligands (Capt, SG, as well as chirally modified phenylethanethiol (PET*)) give rise to distinct chiroptical features. The high thermal stability and distinct optical properties of Au₂₅(Capt)₁₈ nanoclusters render this material quite promising for biological applications.