The extraction of molybdenum and vanadium from weak-acidic sulfate and chloride media by bis(2-ethylhexyl) monothiophosphoric acid (D2EHTPA) and bis (2-ethylhexyl) phosphoric acid (D2EHPA) was investigated. The cationic species of the metals, such as MoO22+, were extracted by both extractants. In the case of vanadium, the supplied VO3- was reduced to VO2+ by contact with the organic phase containing D2EHTPA, and this extractant was partially oxidized to disulfide, While molybdenum was found to be more extractable than vanadium by both extractants, the separation factor of the metals by using D2EHTPA was greater than in the case using D2EHPA, especially when VO3- was used as feed. The oxidized D2EHTPA containing disulfide enhanced the extractability of molybdenum and vanadium. However, the separation factor of the metals decreased with the formation of disulfide. It is important to reduce V(V) to VO2+ prior to extraction in order to minimize the oxidation of D2EHTPA for separation and repeated use of the extractant.