OBJECTIVES: To evaluate the efficacy of pulsed signal therapy (PST) in reducing pain and increasing function in dogs with osteoarthritis (OA) using a randomized, blinded, controlled clinical trial. STUDY DESIGN: Randomized, controlled, blinded clinical trial. ANIMALS: Adult dogs (n = 60) with moderate-to-severe clinical signs of OA. METHODS: Dogs were randomized by age into 2 groups: dogs ≥ 9 years and dogs < 9-years old. The control group received 1 hour of rest in hospital for 9 consecutive days and dogs in the treatment group received PST for 1 hour on 9 consecutive days. Goniometry and gait analysis were performed, and the Canine Brief Pain Inventory (CBPI) questionnaire was given to the owners to fill out without supervision. Outcome measures were repeated at the end of treatment (Day 11) and 6 weeks after beginning treatment (Day 42). RESULTS: The PST group performed significantly better than the control group as measured by the CBPI Severity and Interference scores (P < .01). Extension (P = .04) and peak vertical force (PVF) (P = .03) were not statistically significant after adjusting for multiple comparisons. CONCLUSIONS: The group receiving PST performed better than the treatment group according to owner assessment.