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BACKGROUND: Pulsed electromagnetic fields, as an important physical therapy, are exactly effective in the treatment of osteoarthritis, but the mechanism has not been fully clarified. OBJECTIVE: To observe the effect of pulsed electromagnetic field on the degeneration of knee joint cartilage in aged rats. METHODS: Eight 6-month-old Sprague-Dawley rats were selected as the young group and were subjected to normal diet with no treatment. Sixteen 22-monthold Sprague-Dawley rats were randomly divided into old group (n=8) and pulsed electromagnetic field group (n=8). The rats in the pulsed electromagnetic field group were subjected to a pulsed electromagnetic field intervention, once a day, 5 days per week for continuous 8 weeks. The rats in the old group were given no treatment. All rats were anesthetized and executed after 8 weeks for the detection of relevant indexes. RESULTS AND CONCLUSION: Compared with the young group, serum type II collagen C-terminal peptide level was increased in the old group (P < 0.05); compared with the old group, serum type II collagen C-terminal peptide level was decreased in the pulsed electromagnetic field group (P < 0.05). Micro-CT showed that the bone volume fraction, bone mineral density, and number of bone trabeculae decreased (P < 0.05) and the trabecular separation increased (P < 0.05) in the tibia of rats in the aged group compared with the young group; and the bone volume fraction, bone density, and number of trabeculae increased (P < 0.05) and the trabecular separation decreased (P < 0.05) in the tibia of rats in the pulsed electromagnetic field group compared with the aged group. The tibial plateau Safranin O-fast green staining showed that the articular cartilage structure of rats in the aged group was disorganized, and the number of chondrocytes was obviously reduced, and the tidal line could not be distinguished. The above results were improved in the pulsed electromagnetic field group. RT-qPCR and western blot assay showed that the mRNA and protein expression levels of matrix metalloproteinase 1, matrix metalloproteinase 13, P53 and P21 in the articular cartilage and subchondral bone of rats were elevated in the aged group compared with the young group (P < 0.05) and decreased in the pulsed electromagnetic field group compared with the old group (P < 0.05). To conclude, pulsed electromagnetic fields may improve osteoarthritis in aged rats by inhibiting chondrocyte senescence, alleviating articular cartilage degradation and inhibiting subchondral bone osteoporosis through suppressing the expression of P53/P21. [ABSTRACT FROM AUTHOR]