We report results of a scanning tunneling microscopy investigation on the reconstruction of GaP(001) surfaces. We have observed a 4x2 structure, accompanied locally with c(8x2) domains, at a surface prepared by using ion sputtering and annealing method. On the contrary, both 2x4 [with local c(2x8)] and 4x2 [with local c(8x2)] structures are obtained by hydrogenation followed by annealing. The former consists of a unit structure of three P dimers plus one dimer vacancy, whereas the latter is a parallel arrangement of zig-zag-chained structures along the [110] direction. It has been shown that the surface hydrogenation before annealing induces new types of reconstruction.