Oral hyaluronic acid has been shown to reduce inflammation and pain in humans with osteoarthritis. Eight Asian small-clawed otters (Aonyx cinerea) and two African spot-necked otters (Hydrictis maculicolis) with varying degrees of osteoarthritic changes identified on radiographs were selected for a randomized, double-blinded, placebo-controlled clinical trial. Animal husbandry staff completed otter mobility assessment (OMA) questionnaires for each animal prior to study commencement and following either oral hyaluronic acid at a loading dose of 4 mg/kg PO SID for 10 d followed by a maintenance dose of 2 mg/kg PO SID for 20 d, or placebo for 30 d. Four veterinarians with experience assessing otters watched randomized videos of otter gaits and assigned a clinical lameness score. Two additional evaluators watched the videos: an experienced veterinarian in small animal practice and a final-year veterinary student. All evaluators for OMA and clinical lameness score were blinded to treatment group. Radiographs performed prior to, and following, the study were assessed by a board-certified radiologist (Dennison). The OMA questionnaire had high reliability coefficients and correlated strongly with clinical gait scores and radiographic assessment. Although hyaluronic acid appears to be safe for use in otters at the dose described, there was no observed significant effect of hyaluronic acid on clinical lameness scores, OMA scores, or radiographic assessment of the limbs. The development of the OMA questionnaire is a promising tool for evaluating lameness in managed-care otters and may be further validated in future studies investigating therapeutics or incorporated as a component of animal welfare assessment.