Abstract A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048 M oxalic acid and 6 × 10 −5 M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at −0.1 V ( vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at −0.30 V, which can be used for determining Mo(VI) in the range 5 × 10 −10−7 × 10 −9 M, with a detection limit of 1 × 10 −10 M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu 2+, Ag + and Au 3+ affect the determination.