| Sekinari Nii | |
| Native Name: | 二井 関成 |
| Office: | Governor of Yamaguchi Prefecture |
| Term Start: | 22 August 1996 |
| Term End: | 21 August 2012 |
| Predecessor: | Tooru Hirai |
| Birth Date: | 20 March 1943 |
| Birth Place: | Mine, Yamaguchi, |
| Alma Mater: | University of Tokyo |
is the former governor of Yamaguchi Prefecture in Japan.
Sekinari Nii was born in Mine, Yamaguchi. He studied in University of Tokyo. After graduation in 1966, he started work in the Ministry of Home Affairs. He was elected as governor of Yamaguchi Prefecture in 1996.