In this study a new selective method for determination of trace amounts of molybdenum by adsorptive stripping voltammetry at pH= 4.5 is proposed. The method is based on adsorptive accumulation of Mo-pyrocatechol violet (PCV) complex onto hanging mercury drop electrode (HMDE) at accumulation potential of +0.10 V (vs Ag/AgCl), followed by reduction of adsorbed species by voltammetric scanning in the potential range of -0.40 and 0.80 V (vs Ag/AgCl) in differential modulation. The reduction peak current at -0.68 V (vs Ag/AgCl) is enhanced by addition of dichromate. The effect of instrumental and chemical variable on the sensitivity of the method were studied and optimized. In the optimum condition the limit of detection was found 0.050 ng mL^-1. The relationship between the peak current and molybdenum concentration is linear in the range of 1.0 – 70.0 ng mL^-1. The relative standard deviations for ten replicate determinations of 40.0 and 25.0 ng mL^-1 Mo(VI) are 0.85 and 1.3%, respectively. The effects of interferences ion were studied and it was found that the method is free from interferences of some common cations. The procedure is applied to the determination of molybdenum in real and synthetic samples with satisfactory recoveries (92.5-104%).