 In August 2003, Castellini was re-signed by UEFA Cup competitor Parma for a reported 3-year contract.At Parma, Castellini played 32 Serie A matches and 3 games in 2003–04 UEFA Cup, in although the club already have young talents likes Daniele Bonera and Paolo Cannavaro, Castellini played regularly along with Matteo Ferrari.During the season, he was call-up to national team for the first time and played against Romania.