| Martti Järventaus | |
| Fullname: | Martti Sakari Järventaus |
| Nicknames: | "Mara" |
| Nationality: | Finnish |
| Strokes: | Breaststroke |
| Club: | Lappeenrannan Uimarit |
| Birth Date: | 16 December 1960 |
| Birth Place: | Kotka, Finland |
| Weight: | 72kg (159lb) |
Martti Järventaus (born December 16, 1960, in Kotka, Finland) is a retired male breaststroke swimmer from Finland. He competed twice for his native country at the Summer Olympics: in 1980 and 1984.