Princess Polyxena of Hesse-Rheinfels-Rotenburg (Polyxena Christina Johanna; 21 September 1706 – 13 January 1735) was the second wife of Charles Emmanuel, Prince of Piedmont whom she married in 1724. The mother of the future Victor Amadeus III, she was queen consort of Sardinia from 1730 until her death in 1735.

King Victor Amadeus II of Sardinia approached her family and proposed a union between Polyxena and Victor Amadeus II's son and heir Charles Emmanuel, Prince of Piedmont. A previous match orchestrated by Agostino Steffani with a daughter of Rinaldo, reigning Duke of Modena had come to nothing. His first wife, Countess Palatine Anne Christine of Sulzbach died on 12 March 1723, less than a year after her marriage and barely a week after giving birth to a son,[Victor Amadeus, Duke of Aosta (7 March 1723-1 August 1725.

Although only two years younger, Polyxena was a niece of Charles Emanuel's first wife, and belonged to the only Roman Catholic branch (since 1652) of the reigning House of Hesse. In fact, she had been nominally a canoness of Thorn since 1720.

The engagement was announced on 2 July 1724, and she wed Charles Emmanuel by proxy on 23 July in Rotenburg. The marriage was celebrated in person at Thonon in Chablais on 20 August 1724.

Her stepson Victor Amadeus, heir after his father and grandfather to the Sardinian crown, died at the age of two, a year after Polyxena's marriage and before she had a child of her own. Nonetheless, she is said to have had a close relationship with her mother-in-law Anne Marie d'Orléans and the two frequented the Villa della Regina outside the capital, where the latter died in 1728.

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