Two-photon resonant four-wave mixing difference frequency generation in potassium vapor has been observed.The infrared wave (ω3) from YAG:Nd3+ laser and the visible wave(ω1) from the tunable dye laser pumped by the second-harmonic of YAG:Nd3+ laser are used as the incident waves.When the energy of the two photons from dye laser equals to the energy defferenco between the high lying state 13s and the ground stare 4s of the potassium atom,a new 4052 coherent wave (ω4=ω1-ω3) is generated.