The use of therapeutic ultrasounds (TUs) is widespread in both human and veterinary medicine. In fact, mechanical vibration is the simplest and purest form of vibratory energy that is applied either in physical therapies or in rehabilitation medicine. In particular, the use of low-frequency TUs to treat equine conditions is a new and evolving field. In the equine industry, osteoarthritis (OA) is one of the most challenging causes of lameness. Despite its prevalence and the advancements in its treatment, there is still no therapy whose results are completely decisive. Little is described in the literature about the use of TUs in horses’ joints, particularly regarding its use to treat OA. For these reasons, the aim of this study was to preliminarily assess the efficacy of low-frequency ultrasound in two horses with metacarpo/metatarso-phalangeal joint OA. The reduction in lameness was significant in both treated cases, pointing to the effective therapeutic action of TUs. However, to better evaluate the long-term effects in athlete horses, it is necessary to include in the research a greater number of cases and a control group.