Oltra, who last season oversaw Deportivo's return to the Spanish top flight, has paid the price for a poor start to the season which leaves the club bottom of the table with just 12 points from 17 matches, reports Xinhua.
Deportivo began the season brightly but that early season form has slipped away and the side from the north-west of Spain have taken just three points from their last eight matches.
"It is a decision that had been taken Dec 21," announced club president Cesar Lendoiro in a press conference Sunday.
Lendoiro confirmed Deportivo's defeat to fellow strugglers, Espanyol in the last game of 2012 had been the final straw.
"We don't like changing coach, but we need to kick-start the season and the change of mentality that comes with a new coach," added the club president.
Oltra is the third coach in the Primera Liga to be sacked this season, following Mauricio Pellegrino (Valencia) and Mauricio Pochettino (Espanyol), who lost their jobs earlier in the season as a result of their sides' respective poor performances.