The elastic constants of orthorhombic betaine calcium chloride dihydrate have been investigated by ultrasonic methods in the range between 300 and 100 K. The phase transition at 169 K is accompanied by a sharp softening of all ultrasonic waves having longitudinal components of the displacement vector, similar to the effects observed at the α-β transition of Li2Ge7O15 and at the V–IV transition of thiourea. The transition at 129 K shows only very weak anomalies like those found in the α-β transition of Te(OH)6·2NH4H2PO4·(NH4)2HPO4. The transitions at 169 K and 129 K are of second order.