Gold nanoparticles with tunable size and shape are effectively synthesized with a femtosecond laser using the seed and growth method by reducing a KAuCl4 solution with polyvinylpyrrolidone (PVP) surfactant as a stabilizer. The sizes of gold nanoparticles, including 7.30 to 9.90, 11.0, 12.0, 14.1, 17.3, 22, 23.0, 24.4, and 27.2 nm, are effectively altered. In addition, the initial shapes of gold nanoparticles (quasi-spherical, triangular, and nanoplate) are also successfully changed. While the reduction effect of an unfocused femtosecond laser can control the size of nanoparticles, the surfactant can influence the growth of nanoparticles and determine their shape. This technology represents a breakthrough for nanoparticle development by not employing strong reducing agents and instead using an environmentally friendly synthesis technique. © 2023 Optica Publishing Group.