Berengar I was a 9th-century nobleman of East Francia, a son of Gebhard, Count of Lahngau, and younger brother of Udo.
With his brothers, Udo and Waldo the Abbot, he took part in the 861 revolt of Carloman of Bavaria, possible his cousin-in-law, against Louis the German.
The revolt was crushed and the three brothers fled with their relative Adalard to the court of the West Frankish king, Charles the Bald, who granted them wardship of the march against the Vikings while the march against the Bretons was granted to Robert the Strong.
Charles, to attain peace, took the march back and gave it to Gauzfrid, a Rorgonid.
A charter of 879 mentions Berengar and his brothers taking part in the foundation of the college of Gemünden.