Objective. The aim of this randomized placebo-controlled trial was to evaluate the beneficial effect of a whole plant extract of Brachystemma calycinum D. Don (BCD) in naturally occurring osteoarthritis (OA) in dogs. Methods. Dogs had stifle/hip OA and poor limb loading based on the peak of the vertically oriented ground reaction force (PVF) measured using a force platform. At baseline, PVF and case-specific outcome measure of disability (CSOM) were recorded. Dogs (16 per group) were then assigned to receive BCD (200 mg/kg/day) or a placebo. The PVF was measured at week (W) 3 and W6. Locomotor activity was recorded throughout the study duration using collar-mounted accelerometer, and CSOM was assessed biweekly by the owner. Results. BCD-treated dogs had higher PVF at W3 and W6 when compared to Baseline (P < 0.001) and at W6 when compared to placebo-treated dogs (P = 0.040). Higher daily duration (P = 0.024) and intensity (P = 0.012) of locomotor activity were observed in BCD-treated dogs compared to baseline. No significant change was observed in either group for CSOM. Conclusions. Treatment with BCD improved the limb impairment and enhanced the locomotor activity in dogs afflicted by naturally-occurring OA. Those preclinical findings provide interesting and new information about the potential of BCD as an OA therapeutic.