Mikalojus Radvila or Mikolaj I nicknamed the Old (Lithuanian: Mikalojus Radvilaitis, Mikalojus II Radvila Senasis, Latin: Nicolaus II Radziwil Priscus) (c. 1450 – 16 July 1509) was a Lithuanian noble. He was known after a patronym Radvilaitis, made of his father's name Radvila, which in turn became a family name of his heirs, Radvilos, later Polonised as Radziwiłł.
Mikalojus had been a regent of Smolensk from 2 December 1481; in 1483 a 10,000-strong army was summoned by him for protection of Smolensk lands. He had been the Castellan of Trakai since 31 May 1488 and regent of Novgorodok, later a regent of Bielsk Podlaski. He was the Voivod of Vilnius since 1492 and the first Grand Chancellor of Lithuania from 1504 until his death in 1509. His sons Jerzy/Jurgis, Mikojal/Mikalojus and Jan/Jonas were the progenitors of the three Radziwill family lines.