Lacticaseibacillus paracasei JM053 has a significant ability to convert soy isoflavones and can be used as a fermentation strain to ferment soymilk, thereby increasing the content of free aglycones in soymilk and thus providing an effective method to alleviate osteoporosis symptoms. This study aims to establish a rat model of osteoporosis induced by dexamethasone (DEX) and clarify the alleviating effect of soymilk fermented with Lacticaseibacillus paracasei JM053 on osteoporosis. Research has shown that fermented soymilk with Lacticaseibacillus paracasei JM053 can inhibit weight loss in rats caused by DEX, regulate the expression of inflammatory factors such as tumor necrosis factor-α (TNF-α) towards normal levels, and increase levels of alkaline phosphatase (ALP) and osteocalcin (OCN) to promote bone synthesis. By observing the microstructure of bone tissue through microCT and Goldner staining, it was found that, compared with the model group, fermented soymilk with Lacticaseibacillus paracasei JM053 can alleviate the damage to bone tissue structure caused by DEX by increasing the number of bone trabeculae and reducing fracture. Fermented soymilk with Lacticaseibacillus paracasei JM053 can alleviate bone metabolism disorders by regulating gut microbiota and metabolite content. This study provides theoretical and data-based support for developing functional products that can alleviate osteoporosis.