Batch-type spectroscopic and continuous potentiometric titration of K₄Mo₂Cl₈ with potassium dichromate in 1 M hydrochloric acid was carried out. Intermediate forms of molybdenum compounds in the oxidation process were determined. It was shown that the oxidation is accompanied by a rearrangement of the complex structure with the formation of trinuclear oxo- and hydroxohalide anions of molybdenum into trinuclear oxo- and hydroxohalide molybdenum anions. The standard reduction potential of the pair E298o(MoVI/Mo3IV=1.003+0.032V was determined.