Diepholz – Nienburg I is an electoral constituency (German: Wahlkreis) represented in the Bundestag.

In the inaugural Bundestag election, it was Lower Saxony constituency 23 in the numbering system.

Originally, the constituency comprised the districts of Grafschaft Diepholz, Melle, and Wittlage.

It also included part of the Nienburg district, specifically the territory which now comprises the Samtgemeinde of Uchte.

The constituency was first held by Rudolf Eickhoff of the German Party (DP), who served from 1949 until 1957.

He was succeeded by Karl Gossel of the Christian Democratic Union (CDU), who served two terms.

Fellow CDU members Günter von Nordenskjöld (1965–72) and Richard Ey (1972–80) then each served two terms.

In 1980, the Social Democratic Party (SPD) won the constituency, and Peter Würtz was its representative for a single term.

In 1998, the SPD's Detlev von Larcher won, and served a single term.