The temperature dependent sound velocity and ultrasonic attenuationof the non-superconducting and ferromagnetic superconductorRuSr2GdCu2O8 (Ru-1212) have been determined through the pulse-echo-overlapultrasonic technique. The absolute elastic moduli and Debye temperatureθD (at∼80 K) are also determined. A step-like elastic anomaly above 200 K was observedand explained in terms of oxygen ordering similar to that in the relatedRBa2Cu3O7−δ system. The acoustic Debye temperature is determined as 528 K and this is higher thanthose for other high temperature superconducting cuprates, which are between 250 and500 K.