The 2009–10 Serie D was the sixty-second edition of the top level Italian non-professional football championship.
After the regular season is complete, teams placed 6th-last through to 3rd-last in each division play a double-leg series (6th-last vs 3rd-last, 5th-last vs 4th-last) where the winners remain in Serie D the following season and the two losers are also relegated to Eccellenza for a total of 4 relegations in each division, 36 in total for the league.
The nine division winners enter a tournament to determine the over-all Serie D champion and is awarded the Scudetto Dilettanti.
Teams placed second through fifth in each division enter a playoff tournament after the regular season as well.
The nine division winners are automatically promoted to Lega Pro Seconda Divisione 2010–11.
Promotion playoffs involved a total of 37 teams; four from each of the nine Serie D divisions (teams placed from 2nd through to 5th) with Matera, winner of Coppa Italia Serie D that is directly admitted to the Semi-final round.