The extraction of mercury(II) from nitric acid solutions by the dithiophosphate compounds CH3(CH2)nS2P(OC6H4)2 (n=0 to 4) has been examined. The best extracting properties were displayed by the liquid compound containing the longest alkyl chain CH3(CH2)4S2P(OC6H4)2 (Pen-DTP) in acidic media. The results indicate the stability of Pen-DTPA in nitric and sulphuric media. Pen-DTP selectively extracted Hg(II) in the presence of some interfering ions such as Cd(II), Pb(II) and Bi(III). The Hg(II) recovery from back-extraction experiments with chloridric acid is higher than 70%. Mostly, this extractant shows a remarkable selectivity in the extraction of mercury (76.6%) in the presence of Ag(I) (9.2%) without using a masking agent.