The phase equilibria in the solid state in the system FeVO 4 -Cu 3 V 2 O 8 and FeVO 4 -CuO have been determined. Based on the obtained DTA and XRD analysis results and some additional research, a phase diagram in the whole subsolidus area of the system CuO-V 2 O 5 -Fe 2 O 3 has been worked out. Eighteen subsidiary subsystems can be distinguished in this ternary system. Basic properties of the obtained phases with howardevansite-and lyonsite-type structure have been investigated by DTA, IR, and SEM methods.