Sergio Kalaj (born 28 January 2000) is a professional footballer who plays as a centre-back for Italian club Frosinone. Born in Italy, he represents Albania internationally.
On 12 September 2020, he joined Serie C club Grosseto on loan.
On 22 July 2021, he joined Carrarese on a permanent basis.
On 13 January 2022, he signed a 4.5-year contract with Frosinone in Serie B.