Danielewicz vel Danilewicz - descendants of Daniel or Danilo. Until the end of 17th century, mainly used by highly ranked nobility in Russia and Polish–Lithuanian Commonwealth.
Danielewicz vel Danilewicz of Ostoja coat of arms was a noble family name in Lithuania and in the Polish–Lithuanian Commonwealth. On the political scene Danielewicz supported the Clan of Ostoja expansion in the 15th century and in Lithuania was one of the closest families related to the Pac family, supporting their way to the suprimacy in Grand Duchy of Lithuania at the end of the 17th century. In medieval times, nobles in Lituania with power of judging like Danielewicz where called barones according to Jan Długosz.
First known boyar of the family is Ratsha, noted in year 1146 as Judge of Kiev. However, some scolars in Russia claim that Ratsha was grandson of Ratibor and that Ratibor was descendant of ruling family of Polabian Slavs
This aristocratic family originally came from one of the oldest boyar families from Novgorod in Russia and moved to Lithuania together with other families of Russian origin, entering the Clan of Ostoja. Notable families that moved from Novgorod together with Danielewicz also entering the Clan of Ostoja are the prince Baratynsky and prince Palecki.
The Danielewicz of Ostoja family are to be found mainly among officials in the districts of Vilnius, Ashmyany, Trakai and Vilkmergė. Sources tell about Daniel that had had two sons and one daughter and of them Dawid Danielewicz was the Judge of Vilnius in the middle of the 15th century. In 1530 Michał Danielewicz was in possession of 10 villages with different economic buildings on the property. His grandson, Jan Karzimierz Danielewicz was deputy to the Sejm from the Vilnius district. Iwaszko Iwanowicz Danielewicz attended at the Royal Court in Kraków year 1511, his brother Fedor attended same court year 1523.