| Official Name: | San Siro |
| Native Name: | San Sir |
| Settlement Type: | Quartier of Milan |
| Pushpin Label Position: | bottom |
| Subdivision Type: | Country |
| Subdivision Name: |  Italy |
| Subdivision Type1: | Region |
| Subdivision Name1: | Lombardy |
| Subdivision Type2: | Metropolitan City |
| Subdivision Name2: | Milan |
| Subdivision Type3: | Comune |
| Subdivision Name3: | Milan |
| Subdivision Type4: | Zone |
| Subdivision Name4: | 7 |
| Unit Pref: | Imperial |
| Timezone: | CET |
| Utc Offset: | +1 |
| Timezone Dst: | CEST |
| Utc Offset Dst: | +2 |
San Siro (San Sir) is a vast district ("quartiere") of Milan, Italy, part of the Zone 7 administrative division of the city. About 5 km north-west of the city centre, it borders the districts of Lampugnano, QT8, FieraMilano, and Trenno.
Until the 19th century, San Siro was a small settlement, on the banks of the Olona river; its centre was in the surroundings of what is now Piazzale Lotto. The area has been radically transformed in the 20th century.
San Siro is a very diverse district, with wide green areas and cemented neighbourhoods, low-income and high-income housing, villas and apartment blocks. Most of the buildings in the area date back to the mid 20th century.
The district is also characterized by prominent sports structures, most notably the Giuseppe Meazza football stadium, home of A.C. Milan and Inter Milan. It also houses the most important Milanese hippodrome, as well as other horse racing-related structures. The Palasport di San Siro arena, mainly used for basketball and volleyball games, was also in this district; it was closed in 1985 when its roof collapsed after a large snowfall.