Synthesis of monodisperse small Au nanoparticles in a controllable manner is of great importance for fundamental science and technical applications. Here, we report a “precursor continuous-supply” strategy for controllable synthesis of 0.9–3.3 nm Au nanoparticles with a narrow size distribution of 0.1–0.2 nm, using a weak reductant to slow-down the reducing rate of AuClPPh3 precursor in ethanol. Time-dependent X-ray absorption and UV-Vis absorption measurements revealed that owing to the joint use of AuClPPh3 and ethanol, the remnant AuClPPh3 was self-supplied and the precursor concentration was maintained at a level near to its equilibrium solubility (ca. 1.65 mmol L−1) in ethanol. Hence the nucleation duration was extended that focused the initial size distribution of the Au clusters. With reaction going on for 58 min, most of AuClPPh3 with a nominal Au concentration of 17.86 mmol L−1 was converted to ethanol-soluble Au clusters with a size of about 1.0 nm, resulting in a high-yield synthesis.