| Runni Saidpur | |
| Settlement Type: | Town/ CD Block |
| Pushpin Map: | India Bihar |
| Pushpin Label Position: | right |
| Pushpin Map Caption: | Location in Bihar, India |
| Coordinates: | 26.383°N 85.4833°W |
| Subdivision Type: | Country |
| Subdivision Name: |  India |
| Subdivision Type1: | State |
| Subdivision Name1: | Bihar |
| Subdivision Type3: | District |
| Subdivision Name3: | Sitamarhi |
| Subdivision Type2: | Region |
| Subdivision Name2: | Mithila |
| Unit Pref: | Metric |
| Elevation M: | 47 |
| Population Density Km2: | auto |
| Demographics Type1: | Languages |
| Demographics1 Title1: | Official |
| Demographics1 Info1: | Maithili, Hindi, Urdu |
| Timezone1: | IST |
| Utc Offset1: | +5:30 |
| Postal Code Type: | PIN |
| Postal Code: | 843328 |
| Area Code Type: | Telephone code |
| Area Code: | 06226 |
| Registration Plate: | BR-30 |
| Blank1 Name Sec1: | Lok Sabha constituency |
| Blank1 Info Sec1: | Sitamarhi |
| Blank2 Name Sec1: | Vidhan Sabha constituency |
| Blank2 Info Sec1: | Runnisaidpur |
| Iso Code: | IN-BR |
Runni Saidpur is a town and a block located in Sitamarhi district, Bihar, India. It is situated on the southern bank of the Lakhandei River. National Highway 77 passes through Runni Saidpur. The regional language is Bajjika dialect of Maithili language.
The village is situated between Lakhandei river in the north and the Bagmati river to the south. This area has been hit by flood many times, though the land is very fertile. It is mostly gangetic plain with alluvial soil. The whole area lies to the south of the Someswar mountain range of the southern Himalayas in the north and the holy Ganges in the south. Summer is moderate and the winter is chilling cold. Runni Saidpur is located at .[1] It has an average elevation of 47m (154feet).
The Runni Saidpur block lies in the southwest corner of the Sitamarhi district. It is bordered by the Belsand and Parsauni blocks to the northwest, Dumra to the north, Bajpatti to the northeast, and Nanpur to the east. On the south, it borders the Minapur and Aurai blocks of the Muzaffarpur district.