Abstract: The complete expressions which are necessary to determine the elastic constants of lead molybdate single crystals （PbMoO₄, briefly called PMO） have been derived from Christoffel equation describing the elastic waves in anisotropic solids. Pulse-Echo-Overlap ultrasonic velocities measurements were made for fourteen different modes on five differently oriented single-crystal specimens. This set of date has been used to calculate its seven independent room-temperature clastic-stiffness constants. In units of 10¹¹ dyn/cm², C₁₁ = 10.459 C₃₃ = 9.244 C₄₄ = 2.608 C66 = 3.522 C₁₂ = 5.473 C₁₃= 5.201 C₁₆ = 1.802.