Abstract: Psocids are now recognized as stored-product pests of substance worldwide. Lack of information exists on resistance of psocids to phosphine (PH3) in the USA. In this study we determined discriminating doses of PH3 for adults of three psocid (Psocoptera: Liposcelididae) species, namely, Liposcelis bostrychophila Badonnel, L. paeta Pearman, and L. decolor (Pearman). Protocols used were modified from the FAO Method No. 16, to determine lethal doses that caused 99% mortality and their 95% confidence intervals for the laboratory susceptible strain of each species. Dose-response studies were conducted by exposing adults of all species to different concentrations of PH3 for 20 hours. Mortality was assessed 24 hours after exposure. Discriminating doses for L. bostrychophila, L. paeta, and L. decolor adults were 46.7, 122.2, and 187.8 ppm, respectively. These data show that the three Liposcelis species responded differently to PH3. The discriminating doses from this study will be used in future research to determine resistance frequencies of field populations of these species.