| Official Name: | Posht Tang-e Sofla Seyyed Reza |
| Native Name: | پشت تنگ سفلي صيدرضا |
| Settlement Type: | village |
| Subdivision Type: | Country |
| Subdivision Type1: | Province |
| Subdivision Name1: | Lorestan |
| Subdivision Type2: | County |
| Subdivision Name2: | Kuhdasht |
| Subdivision Type3: | Bakhsh |
| Subdivision Name3: | Tarhan |
| Subdivision Type4: | Rural District |
| Subdivision Name4: | Tarhan-e Sharqi |
| Population As Of: | 2006 |
| Population Total: | 180 |
| Population Density Km2: | auto |
| Timezone: | IRST |
| Utc Offset: | +3:30 |
| Timezone Dst: | IRDT |
| Utc Offset Dst: | +4:30 |
Posht Tang-e Sofla Seyyed Reza (Persian: پشت تنگ سفلي صيدرضا, also Romanized as Posht Tang-e Soflá Seyyed Rez̤ā) is a village in Tarhan-e Sharqi Rural District, Tarhan District, Kuhdasht County, Lorestan Province, Iran. At the 2006 census, its population was 180, in 36 families.