This invention relates to a process for the preparation of 5-amino-1-phenyl-3-cyano-4-trifluoromethyl sulphinyl pyrazoles as defined by Formula- I, wherein: Rl = trif luoromethyl or trif luoromethoxy, and R2, R3 = individually hydrogen, chlorine or bromine , the process comprising the step of oxidizing a compound of Formula- II, wherein: Rl = trifluoromethyl or trif luoromethoxy, and R2, R3 = individually hydrogen, chlorine or bromine , in a medium comprising at least one oxidizing agent and trichloro acetic acid, and/or the reactions product (s) of the at least one oxidizing agent and trichloro acetic acid, and at least one melting point depressant. The preferred pyrazole is Fipronil, preferably prepared using hydrogen peroxide and dichloro acetic acid at room temperature .