Molybdenum was anodized at different current densities (10−4–10−2 A cm−2) in various aqueous solutions. Potential-time curves obtained in strong acid solutions are similar to those usually reported for the valve metals, and the anodization kinetics were found to obey the familiar exponential law $$i = A \exp BH$$ and also to obey the empirical relation, $$(dE/dt)_i = a(i)^b $$ Using both polarization and capacitance measurements, it was found that the field strength,H, the electrolytic parametersA andB and the constantsa andb are comparable with those previously reported for many valve metals. Except in strong acid solutions,E-time curves showed an induction period before oxide formation. The duration time of the induction period,ti, was found to increase with decrease of solution acidity and current density and with increase of temperature. Although chloride ion may act as a depolarizer,ti was found to decrease with increase of chloride ion concentration, probably by increasing the anodization field strength.