Low-intensity ultrasound (LIUS) is a special type of sonic waves that can stimulate and/or regulate various cellular functions, and thereby regulate status of related diseases. In our previous study, LIUS was shown to relieve pain and progression of osteoarthritis (OA) in a rabbit model, when co-treated with hyaluronan. In this study, we investigated the LIUS effect on the repair of OA in vitro and in a rabbit OA model at the molecular level. The rabbit OA model was created by dissecting the anterior cruciate ligaments (ACLs) and medial meniscus on the right knee joints of adult male New Zealand white rabbits. The left knee joint was mock-operated as a sham control. The right knee joints with surgery were mock-treated or treated with LIUS every day for 10 min at a frequency of 1 MHz and an intensity of $100 mW/cm2$. The rabbits were sacrificed at 2 and 4 weeks postoperatively. In the histochemical analyses of joint cartilages, LIUS was shown to reduce progression of OA-phenotypes such as loss of cells, decrease in the levels of sulfated glycosamionoglycans (GAGs) and type II collagen, and increase in the expression of type X collagen and matrix metalloproteinases (MMP-9 and MMP-13). In the experiment in vitro, rat chondrocytes were treated with interleukin-1? (IL-1 beta) to induce OA-phenotypes. Then, LIUS was treated every day for 20 min from day 0 at varying intensities of $30 mW/cm2$, $70 mW/cm2$, and $100 mW/cm2$. When analyzed at 1, 2, and 3 days, IL-1 beta reduced the expression of cartilage-specific genes of type II collagen and aggrecan and induced the expression of type X collagen, MMP-9 and MMP-13. In contrast, co-treatment of LIUS reversed the activity of IL-1 beta particularly at $30 mW/cm2$ and $70 mW/cm2$. These results showed that LIUS inhibited the changes in the expression of OA-related genes. The results of this study confirmed our previous result on the LIUS effect at the molecular level and further suggest that LIUS could be a potent intervention to OA and cartilage disorders in clinics.