Castillo returns to Greece with Aris
The 26-year-old Mexico international had a loan spell with Manchester City in 2008 and scored 30 goals during a seven-year spell with Olympiakos Pireaus.
"I am coming to a big club such as Aris with a great hopes of playing good football. For me this constitutes an opportunity to return to Greece and show what I can achieve," Castillo said in a statement.
"I will give everything for Aris to achieve its targets in Greece and Europe."
Aris are eighth in the 16-team league with 23 points from 18 games.