4-Chlorophenoxyacetic acid (4-CPA) is a plant growth regulator that offers several benefits. When applied to mulberry leaves, it promotes growth and enhances the content of flavonoid compounds. These flavonoids, including rutin, chlorogenic acid, isoquercitrin, and astragalin, contribute to the leaves’ antioxidant properties. Additionally, 4-CPA treatment increases shoot and bud numbers, leaf weight, and area, making it valuable for improving the medicinal quality of mulberry leaves.