Amoroso started his career at homeland club Guarani FC at 1992. In July 1992, he was loaned to a Japanese outfit Verdy Kawasaki (J.League Division 1), winning two J-League titles, and returned to Guarani FC two years later, finishing the 1994 Campeonato Brasileiro Série A as the season's top scorer. In 1996, he transferred to Flamengo, but he came to prominence playing in the Italian Serie A for unfashionable Udinese in the late-1990s. There he starred alongside Oliver Bierhoff in a side which played an adventurous 3–4–3 formation, finishing his first season with the club in third place in Serie A. When the league's top scorer Oliver Bierhoff left the club for A.C. Milan in 1998, many thought Udinese Calcio would struggle to repeat their success, but that very next season Amoroso himself became the focus of the team, and was the top scorer in Serie A with 22 goals. The following season, he transferred to the defending UEFA Cup and Coppa Italia champions Parma for an astounding €30 million. Although the team started the season strongly, winning the 1999 Supercoppa Italiana, Parma never quite fulfilled their potential to win the league title, and Amoroso was not able to match the form he managed with Udinese due to recurring injury problems; the club did manage to reach the 2001 Coppa Italia final, however.