We report a facile, high yielding synthetic method for preparing truly monodisperse Au(38)(SC(2)H(4)Ph)(24) nanoclusters. The synthetic approach involves two main steps: first, glutathionate (-SG) protected polydisperse Au(n) clusters (n ranging from 38 to approximately 102) are synthesized by reducing Au(I)-SG in acetone; subsequently, the size-mixed Au(n) clusters react with excess phenylethylthiol (PhC(2)H(4)SH) for approximately 40 h at 80 degrees C, which leads to Au(38)(SC(2)H(4)Ph)(24) clusters of molecular purity. Detailed studies by mass spectrometry and UV-vis spectroscopy explicitly show a gradual size-focusing process occurred in the thermal etching-induced growth process. The formula and molecular purity of Au(38)(SC(2)H(4)Ph)(24) clusters are confirmed by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometry, and size-exclusion chromatography. The optical and electrochemical properties of Au(38)(SC(2)H(4)Ph)(24) clusters show molecule-like behavior and the HOMO-LUMO gap of the cluster was determined to be approximately 0.9 eV. The size focusing growth process is particularly interesting and may be exploited to synthesize other robust gold thiolate clusters.