The present invention refers to a process for the preparation of pyrazole derivatives of formula (I) wherein W is nitrogen or CR1, R1, R2, R4 and R5 are each independently selected from hydrogen, halogen, C1-C6-alkyl, C1-C6-haloalkyl, C1-C6-alkoxy, C1-C6-haloalkoxy, R7S(O)n, nitro, cyano, and pentafluorothio； R3 is hydrogen, halogen, C1-C6-alkyl, C1-C6-haloalkyl, C1-C6-alkoxy, C1-C6-haloalkoxy, R7S(O)n, nitro, cyano, pentafluorothio or phenyl which is unsubstituted or substituted by 1 to 5 members of the group consisting of halogen, C1-C6-alkyl, C1-C6-haloalkyl, C1-C6-alkoxy, C1-C6-haloalkoxy, R7S(O)n, nitro, cyano, and pentafluorothio which are the same or different； R7 is C1-C6-alkyl or C1-C6-haloalkyl； and n is 0, 1, or 2； characterized in that hydrazines of formula (II) wherein W, R2, R3, R4, and R5 are as defined for pyrazole derivatives of formula (I), are reacted with a compound of formula (III)
