A phosphorus-containing polymer includes a structural unit derived from a first monomer and a structural unit derived from a second monomer. A resin composition contains the phosphorus-containing polymer, and an article is made from the resin composition. The resin composition includes: 100 parts by weight of a free radical polymerizable resin, the free radical polymerizable resin including an unsaturated CC double bond-containing polyphenylene ether resin, a maleimide resin, a polyolefin or a combination thereof; and 12 parts by weight to 100 parts by weight of the phosphorus-containing polymer. The resin composition or the article made therefrom may achieve improvements in one or more properties including glass transition temperature, flame retardancy, dissipation factor, peeling strength, percent of thermal expansion in Z-axis, laminate appearance, heat resistance after moisture absorption and multi-layer board heat resistance.

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