| Date: | 6–12 December |
| Edition: | 2nd |
| Draw: | 32S / 16D |
| Surface: | Hard (Indoor) |
| Location: | Forlì, Italy |
| Champs: |  Pavel Kotov |
| Champd: |  Alexander Erler / Lucas Miedler |
| Before Year: | 2021 |
| Before Name: | Città di Forlì II |
| Main Name: | Città di Forlì – Trofeo MBM Città di Forlì |
| After Name: | Città di Forlì |
The 2021 Città di Forlì III was a professional tennis tournament played on hard courts. It was the second edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Forlì, Italy between 6 and 12 December 2021.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Maxime Cressy | 122 | 1 | ||
 Italy | Federico Gaio | 153 | 2 | |
| Italy | Salvatore Caruso | 157 | 3 | |
 Belgium | Zizou Bergs | 185 | 4 | |
 Bosnia and Herzegovina | Mirza Bašić | 231 | 5 | |
 Ukraine | Vitaliy Sachko | 260 | 6 | |
| Italy | Andrea Vavassori | 262 | 7 | |
| Italy | Andrea Arnaboldi | 266 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry into the singles main draw using protected rankings:
The following player received entry into the singles main draw as an alternate:
The following players received entry from the qualifying draw:
Daniele Capecchi Savriyan Danilov Luca Potenza
Keegan SmithSee main article: 2021 Città di Forlì III – Singles.
Pavel Kotov def. Andrea Arnaboldi 6–4, 6–3.See main article: 2021 Città di Forlì III – Doubles.
Alexander Erler / Lucas Miedler def. Marco Bortolotti / 
Sergio Martos Gornés 6–4, 6–2.