The formation of laser-induced periodic surface structures (LIPSS) on mirror-polished 304-grade stainless steel sheets with dimensions 25 mm × 25 mm × 0.8 mm upon irradiation with picosecond laser pulses in air and water environments at different wavelengths, number of pulses, and laser energy densities was investigated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the LIPSS. Tunable periodicity of the LIPSS was observed in both media at different wavelengths and fluence. Fluence was shown to be the main formation parameter of LIPSS; however, the medium was also demonstrated to play an important role. Our results show that LIPSS can be successfully generated on stainless steel in a single-step process and that they can be easily modified by adjusting laser parameters.