| Competition: | Prima Categoria |
| Season: | 1920–21 |
| Winners: | Pro Vercelli 6th title |
| Prevseason: | 1919–20 |
| Nextseason: | 1921–22 (FIGC) → 1921–22 (CCI) |
The 1920–21 Prima Categoria season was won by Pro Vercelli.
Struggles between minor and major clubs continued, more, they went out of control. The regional FAs expanded the championship to 64 clubs. The preliminary regional phase became the bulk of the tournament, with even sixteen matchdays and regular regional football champions, while the following national phase was reduced to a spring tournament of eight matchdays.
The main tournament was completely divided in five independent sections, and each region had its own football champions. The spots to the national championship were divided according to the agreements between the Regional FAs.
National championship was split in four groups of four clubs. Group winners advanced to the final four. The whole tournament could have twenty-two matchdays.
The experimental Southern groups had their own special regulations.
Regional FAs agreed to expand the league to 64 clubs. They variously chose to promote, re-elect, or invite clubs to fill the spots they had been granted to.
Rivarolese and Sestrese were admitted to the 1a Categoria.
Rivarolese was demoted by the Federazione Italiana Giuoco Calcio after incidents caused by its supporters during the match Rivarolese-Savona (0–2). Rivarolese's remaining matches were all considered forfeits. The side was readmitted to the championship for the following season.
Played on 20 February 1921 in Vercelli.
US Torinese qualified for the Northern Italy semifinals. Casale resigned from the FIGC.
Played on 20 March 1921 in Turin.
The match was voided due to irregularities.
Played on 27 February 1921 in Padua.
Played on 6 February and 13 March 1921 to determine Emilia's regional champion.
Since the aggregate rule wasn't applied, a tie-breaker was needed.
Played on 2 and 20 February 1921.
Played on ? in ?.
Played on 3 July 1921 in Milan.
Played on 26 June 1921 in Vercelli.
A tie-breaker was due, but both Legnano and Torino decided to retire from the championship and to resign from the FIGC.
Played on 10 July 1921 in Turin.
Bologna F.C. advanced directly to Round 2 due to Torino and Legnano's retirement. Alessandria resigned from the FIGC.
Played on 17 July 1921 in Livorno.Bologna resigned from the FIGC.
See main article: Football in Southern Italy in 1920–21. An experimental amatorial tournament was played in Southern Italy.
Played on 3 July 1921 in Bologna.Livorno resigned from the FIGC.
Played on 24 July 1921 in Turin.Both teams resigned from the FIGC.